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Obstetric Imaging

Obstetric imaging refers to imaging of the female reproductive tract and developing fetus during pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care. Ultrasonography is the 1st-line imaging modality during pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care as it does not emit radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma; thus, it is the safest option for the developing fetus. Obstetricians depend heavily on ultrasound for the detection, monitoring, and assessment of several maternal and fetal conditions without radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma exposure Exposure ABCDE Assessment. For example, congenital Congenital Chorioretinitis fetal anomalies, abnormal placentation, poor fetal growth, and abnormal fluid volumes can all be thoroughly assessed using ultrasound. Radiation-emitting imaging modalities ( X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests, CT) are typically reserved for nonobstetric emergency situations.

Last updated: 6 May, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Introduction

Obstetric imaging refers to imaging of the female reproductive tract and developing fetus during pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care.

  • Except in rare cases, obstetric imaging is performed via ultrasound.
  • Ultrasound has the following advantages:
    • No radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma exposure Exposure ABCDE Assessment
    • Ability to view real-time images of the moving fetus
    • Relatively low cost and wide availability
  • In rare circumstances, obstetric imaging can be obtained via other modalities (e.g., MRI).
  • Nonobstetric imaging in pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care should be ordered judiciously to avoid unnecessary radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma exposure Exposure ABCDE Assessment to the developing fetus.

Types of obstetric imaging exams

There are 2 primary types of obstetric imaging exams:

  • Abdominal obstetric ultrasound: good for assessing the fetus, placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity, fluid, and uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy starting in the late 1st trimester through delivery
  • Transvaginal ultrasound:
    • Good for assessing the cervix Cervix The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Externally, the cervix is lined by stratified squamous cells; however, the cervical canal is lined by columnar epithelium. Uterus, Cervix, and Fallopian Tubes: Anatomy throughout pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
    • Better for evaluating the fetus and uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy in early pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care

Specific studies

Several specific types of studies can be performed. All are ultrasound exams and may be either abdominal or transvaginal.

  • Dating scan: for the measurement of either the gestational sac or the fetus itself to help establish the gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care and calculate the estimated date of delivery Estimated Date of Delivery Pregnancy: Diagnosis, Physiology, and Care ( EDD EDD Pregnancy: Diagnosis, Physiology, and Care)
  • Anatomy survey: to assess the anatomy of both the fetus and the mother
  • Growth scan: Specific measurements are used to calculate the estimated weight of the fetus.
  • Position assessment: to determine the direction in which the fetus is facing within the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy in preparation for delivery
  • Fluid assessments: measurements to help estimate the amount of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity
  • Biophysical profile:
    • Assessment of fetal well-being
    • Determination of different types of fetal movements combined with a fluid assessment
  • Doppler Doppler Ultrasonography applying the doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. Ultrasound (Sonography) studies:
    • Evaluation of the pulse waveforms in specific fetal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology to assess fetal well-being
    • May demonstrate signs of fetal anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types or uteroplacental insufficiency Uteroplacental Insufficiency Uteroplacental insufficiency may be acute or chronic and refers to the inability of the placenta to deliver a sufficient supply of O2 and nutrients to the fetus Placental Abnormalities

Indications for Obstetric Imaging

Routine prenatal care Prenatal care Prenatal care is a systematic and periodic assessment of pregnant women during gestation to assure the best health outcome for the mother and her fetus. Prenatal care prevents and identifies maternal and fetal problems that adversely affect the pregnancy outcome. Prenatal Care

Obstetric imaging is part of routine prenatal care Prenatal care Prenatal care is a systematic and periodic assessment of pregnant women during gestation to assure the best health outcome for the mother and her fetus. Prenatal care prevents and identifies maternal and fetal problems that adversely affect the pregnancy outcome. Prenatal Care, including:

  • 1st trimester:
    • Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care confirmation
    • Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care dating/establishing the EDD EDD Pregnancy: Diagnosis, Physiology, and Care
    • Determining the number of fetuses
    • Determining chorionicity of multiple gestations (e.g., monochorionic diamniotic twins)
    • A component of fetal aneuploidy screening Screening Preoperative Care
    • Looking for abnormalities of the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy and/or ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries: Anatomy
  • 2nd trimester:
    • Fetal anatomic survey ( screening Screening Preoperative Care for congenital Congenital Chorioretinitis anomalies)
    • Assessing placentation:
      • Location of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity (confirming it is away from the internal cervical os)
      • Looking for signs of placental invasion into the myometrium (e.g., placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity accreta spectrum (PAS))
    • Assessing the cervical length
  • 3rd trimester:
    • Estimating fluid volumes
    • Determining fetal position Fetal position Direction of the fetal head in relation to the maternal pelvis in vertex presentations Normal and Abnormal Labor prior to delivery

Monitoring higher-risk pregnancies

  • Assessing fetal growth (growth scans)
  • Following the development of congenital Congenital Chorioretinitis anomalies
  • Assessing fetal status in higher-risk pregnancies (e.g., biophysical profile or doppler Doppler Ultrasonography applying the doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. Ultrasound (Sonography) studies in an individual with known preeclampsia Preeclampsia A complication of pregnancy, characterized by a complex of symptoms including maternal hypertension and proteinuria with or without pathological edema. Symptoms may range between mild and severe. Pre-eclampsia usually occurs after the 20th week of gestation, but may develop before this time in the presence of trophoblastic disease. Hypertensive Pregnancy Disorders)
  • Following fetuses at high risk for developing hydrops fetalis Hydrops fetalis Abnormal accumulation of serous fluid in two or more fetal compartments, such as skin; pleura; pericardium; placenta; peritoneum; amniotic fluid. General fetal edema may be of non-immunologic origin, or of immunologic origin as in the case of erythroblastosis fetalis. Parvovirus B19

Emergency care

Individuals may present with a number of symptoms in pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care that warrant ultrasound evaluation:

  • Bleeding and/or pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways in early pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care:
    • Rule out ectopic and molar pregnancies.
    • Assess fetal viability/evaluate for potential fetal loss (i.e., spontaneous abortion Spontaneous abortion Spontaneous abortion, also known as miscarriage, is the loss of a pregnancy before 20 weeks’ gestation. However, the layperson use of the term “abortion” is often intended to refer to induced termination of a pregnancy, whereas “miscarriage” is preferred for spontaneous loss. Spontaneous Abortion).
  • Bleeding in later pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care: Look for signs of placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage ( premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis separation of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity).
  • Preterm contractions or pelvic pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways:
    • Cervical length measurement to assess for cervical insufficiency Cervical insufficiency Cervical dilation without contractions (not labor), due to structural weakness of the cervix Preterm Labor and Birth or signs of cervical change
    • Growth scan: important to help the pediatrics team prepare for delivery and provide appropriate counseling to parents (especially in anticipated cases of very premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis delivery)
  • Loss of fluid: Assess fluid levels.
  • Decreased fetal movement: biophysical profile for the assessment of fetal movement

During procedures

Ultrasound is often used to assist the physician during procedures such as:

Performing an Obstetric Ultrasound

Ultrasound exam technique

  • Positioning of the individual:
    • Abdominal scans:
      • Supine with access to the lower abdomen
      • 2nd/3rd trimesters: A hip roll (rolled-up sheet) should be placed under 1 of the hips of the individual so that they are not lying flat on their back.
    • Transvaginal scans: lower lithotomy
  • Tips for obtaining good images:
    • Maximize contact between the individual’s skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions and ultrasound probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography).
    • Use plenty of ultrasound gel.
  • Depth and gain:
    • Determines the field of view and echogenicity characteristics of the tissue
    • In early pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care, the entire gestational sac should be viewed at once.

Components of the exam

Components that should be assessed during all 2nd and 3rd trimester obstetric ultrasounds:

  • Fetal heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology
  • Fetal position Fetal position Direction of the fetal head in relation to the maternal pelvis in vertex presentations Normal and Abnormal Labor: What part of the fetus is in the lower uterine segment (and thus will deliver 1st)?
  • Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume
  • Placental location in relation to the cervix Cervix The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Externally, the cervix is lined by stratified squamous cells; however, the cervical canal is lined by columnar epithelium. Uterus, Cervix, and Fallopian Tubes: Anatomy
  • Any other objective of the study (e.g., anatomic survey, growth assessment, etc ETC The electron transport chain (ETC) sends electrons through a series of proteins, which generate an electrochemical proton gradient that produces energy in the form of adenosine triphosphate (ATP). Electron Transport Chain (ETC).)

Preparing for general image interpretation

Prior to interpretation of any image, the physician should take certain preparatory steps. The same systematic approach should be followed every time.

  • Confirm name, date, and time on all images.
  • Review the individual’s medical history and physical examination findings.
  • Confirm that the appropriate exams and techniques that can best assess the suspected pathology were ordered/performed.
  • Determine orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment of the image.
  • Have any other previously obtained relevant images available for comparison handy.

Normal Findings on Obstetric Ultrasound

Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care confirmation

  • Gestational sac:
    • Earliest sign of intrauterine pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care, seen around 4.5‒5 weeks gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care (wga)
    • Should be visible in the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy if the quantitative serum β-hCG is > 2,000
    • Anechoic Anechoic A structure that produces no echo at all (looks completely black) Ultrasound (Sonography), well-defined round structure
    • Surrounded by an echogenic rim, representing the decidual reaction
  • Yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development:
    • Hyperechoic Hyperechoic A structure that produces a high-amplitude echo (lighter grays and white) Ultrasound (Sonography) ring-like structure within the gestational sac
    • 1st seen at approximately 5‒6 wga and disappears at approximately 10 wga
  • Fetal pole:
    • The fetus itself
    • Visible around 5.5‒6 wga
    • A heartbeat is usually visible as soon as the fetal pole is visible.
  • Corpus luteum cyst Corpus Luteum Cyst Gynecological Imaging:
    • An adnexal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast representing the follicle from which the oocyte ovulated, which persists throughout the 1st trimester of pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
    • Produces progesterone Progesterone The major progestational steroid that is secreted primarily by the corpus luteum and the placenta. Progesterone acts on the uterus, the mammary glands and the brain. It is required in embryo implantation; pregnancy maintenance, and the development of mammary tissue for milk production. Progesterone, converted from pregnenolone, also serves as an intermediate in the biosynthesis of gonadal steroid hormones and adrenal corticosteroids. Gonadal Hormones, which is vital for survival of the pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
    • Sonographic appearance:
      • Cyst may be simple or complex.
      • Typically surrounded by ↑ vasculature, seen on Doppler Doppler Ultrasonography applying the doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. Ultrasound (Sonography) studies as a circumferential rim of color known as the “ring of fire”

Determining viability

Establishing that a pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care is viable requires:

  • Intrauterine location:
    • Should be within the main uterine body endometrium Endometrium The mucous membrane lining of the uterine cavity that is hormonally responsive during the menstrual cycle and pregnancy. The endometrium undergoes cyclic changes that characterize menstruation. After successful fertilization, it serves to sustain the developing embryo. Embryoblast and Trophoblast Development
    • At least a gestational sac and yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development must be seen in order to establish the pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care location (a gestational sac alone is not enough).
  • A detectable fetal heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology, usually between about 120‒160 per minute (may be slightly higher at certain points in early pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care)
Calculation of the fetal heart rate by ultrasound

Calculation of the fetal heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology by ultrasound


Image by Hetal Verma.

Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care dating via ultrasound

  • 1st trimester obstetric ultrasound is the best and the most accurate tool to estimate gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care and calculate the EDD EDD Pregnancy: Diagnosis, Physiology, and Care.
    • Most accurate in the 1st trimester
    • Ultrasound gets less and less accurate as gestation progresses due to normal genetic variations (e.g., height of parents) and due to effects of the intrauterine environment (e.g., smokers have worse placental perfusion).
  • 1st-trimester dating:
  • 2nd and 3rd trimester dating:

Determining the number of embryos

  • The uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy should be fully evaluated in all planes to get an accurate fetal count.
  • Multiple gestation: when > 1 fetus is present
    • Twins
    • Higher-order multiples (e.g., triplets, quadruplets, etc ETC The electron transport chain (ETC) sends electrons through a series of proteins, which generate an electrochemical proton gradient that produces energy in the form of adenosine triphosphate (ATP). Electron Transport Chain (ETC).)

Determining chorionicity in multiple gestations

Chorionicity describes whether the fetuses share a chorion Chorion The outermost extraembryonic membrane surrounding the developing embryo. In reptiles and birds, it adheres to the shell and allows exchange of gases between the egg and its environment. In mammals, the chorion evolves into the fetal contribution of the placenta. Placenta, Umbilical Cord, and Amniotic Cavity or amnion Amnion The innermost membranous sac that surrounds and protects the developing embryo which is bathed in the amniotic fluid. Amnion cells are secretory epithelial cells and contribute to the amniotic fluid. Placenta, Umbilical Cord, and Amniotic Cavity. Chorionicity can be established by different ultrasound findings in different types of twins:

  • Dichorionic/diamniotic twins (each twin is in their own chorioamnion and has their own placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity): 
    • Thick intertwin membrane
    • Lambda sign: a thick, triangular protrusion of tissue leading up to the intertwin membrane
    • 2 separate placentas (however, if they are right next to each other, they may appear as a single placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity)
  • Monochorionic/diamniotic (twins are in their own amniotic sac, but share a chorion Chorion The outermost extraembryonic membrane surrounding the developing embryo. In reptiles and birds, it adheres to the shell and allows exchange of gases between the egg and its environment. In mammals, the chorion evolves into the fetal contribution of the placenta. Placenta, Umbilical Cord, and Amniotic Cavity and placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity):
    • Thin intertwin membrane
    • T sign: The intertwin membrane comes straight into the sac wall, without the thick triangular protrusion of tissue that is seen in dichorionic diamniotic twins.
    • Single placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity
  • Monochorionic/monoamniotic (twins share a chorioamnion and placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity)
    • No intertwin membrane
    • Single placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity

Anatomic survey

A complete anatomic survey assesses both the maternal reproductive tract and looks for fetal anomalies. Some of the important features evaluated include:

  • Maternal anatomy:
    • Cervical length: should be > 25 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma until at least 24 wga
    • Presence of any uterine fibroids Uterine Fibroids Gynecological Imaging distorting the cavity, or in the lower uterine segment, which may be in the way of a potential cesarean incision
    • Adnexal masses Adnexal Masses Female Genitourinary Examination
  • Placental and umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity assessment:
    • Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity:
      • Should not cover the internal cervical os
      • Should not invade into the underlying myometrium
    • Umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity:
      • Should have 3 visible vessels
      • Should insert near the middle of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity and at the fetal umbilicus
      • Vessels should be surrounded by protective jelly all the way down to the placental insertion.
  • Fetal anatomy: Multiple structures, including all major organs, are measured and assessed.
    • Brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification 
    • Face
    • Heart/ lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy, including 4-chamber and outflow-tract views of the heart
    • Abdomen
    • Limbs
    • Genitalia

Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity assessment

Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity can be assessed in 2 ways:

  • Single deepest pocket (SDP):
    • Measures the single deepest vertical pocket of fluid 
    • The measured pocket must be free of the umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity and fetal parts.
    • Normal range (2nd and 3rd trimesters): 2‒8 cm
  • Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity index (AFI):
    • Divide the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy into 4 quadrants and obtain an SDP for each quadrant; the AFI is the sum of the 4 SDP measurements.
    • Normal range (2nd and 3rd trimesters): 5‒24 cm

Summary of normal findings on obstetric ultrasound

  • Single intrauterine pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
  • Fetal heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology between 120 and 160 per minute
  • No significant congenital Congenital Chorioretinitis anomalies identified
  • Normal placental attachment Attachment The binding of virus particles to virus receptors on the host cell surface, facilitating virus entry into the cell. Virology, away from the cervical os
  • 3-vessel umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity
  • Normal volume of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity
  • Cervical length > 25 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma until at least 24 wga
  • Appropriate fetal weight for gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care
  • Vertex fetal positioning in the late 3rd trimester (not important earlier)

Abnormal Findings on Obstetric Ultrasound

Numerous abnormalities can be identified on obstetric ultrasound.

Abnormal/nonviable pregnancies

Threatened and missed abortions:

  • Threatened abortion Threatened abortion Uterine bleeding from a gestation of less than 20 weeks without any cervical dilatation. It is characterized by vaginal bleeding, lower back discomfort, or midline pelvic cramping and a risk factor for miscarriage. Spontaneous Abortion:
    • A pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care with clinical signs indicating the possibility of a miscarriage Miscarriage Spontaneous abortion, also known as miscarriage, is the loss of a pregnancy before 20 weeks’ gestation. However, the layperson use of the term “abortion” is often intended to refer to induced termination of a pregnancy, whereas “miscarriage” is preferred for spontaneous loss. Spontaneous Abortion (e.g., bleeding and cramping)
    • Fetal heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology (FHR) will still be present.
    • Hyper- or hypo-echoic areas may be visible near the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity or behind the membranes, suggestive of bleeding.
  • Missed abortion Missed abortion The retention in the uterus of a dead fetus two months or more after its death. Spontaneous Abortion: 
    • A fetus is present in the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy, but no longer viable.
    • FHR will be absent.

Ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care:

An ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care is characterized by implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week outside the uterine cavity. Ultrasound findings include:

  • Heterogeneous adnexal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
  • Tubal ring sign: an echogenic ring separating the ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care from the ovary 
  • Pseudogestational sac:
    • Cystic Cystic Fibrocystic Change sac within the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy, with no embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week
    • Decidual reaction present: thickened echogenic endometrium Endometrium The mucous membrane lining of the uterine cavity that is hormonally responsive during the menstrual cycle and pregnancy. The endometrium undergoes cyclic changes that characterize menstruation. After successful fertilization, it serves to sustain the developing embryo. Embryoblast and Trophoblast Development surrounding the intrauterine sac (because pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types are still being produced by the ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care)
    • Misleading, because it can appear identical to an early gestational sac before the yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development appears
  • No identifiable pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care when the HCG is > 2,000
  • Free peritoneal fluid, possibly with low-level internal echos suggests hemorrhage from ruptured ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care.
  • Note on heterotopic Heterotopic Transplantation of tissue typical of one area to a different recipient site. The tissue may be autologous, heterologous, or homologous. Organ Transplantation pregnancies (twin gestations with 1 fetus in the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy and 1 ectopic):
    • Possible, but exceedingly rare
    • If an intrauterine gestation is identified, the adnexa should still be evaluated for masses; if it is not seen, heterotopic Heterotopic Transplantation of tissue typical of one area to a different recipient site. The tissue may be autologous, heterologous, or homologous. Organ Transplantation pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care can be excluded.
Transvaginal ultrasound

Transvaginal ultrasound showing an empty uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy (left) with endometrial thickening and an echogenic mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast (right) representing an ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care adjacent to normal ovarian tissue

Image by Hetal Verma.

Molar pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care:

Molar pregnancies are a type of gestational trophoblastic disease Gestational trophoblastic disease Gestational trophoblastic diseases are a spectrum of placental disorders resulting from abnormal placental trophoblastic growth. These disorders range from benign molar pregnancies (complete and partial moles) to neoplastic conditions such as invasive moles and choriocarcinoma. Gestational Trophoblastic Disease that occur due to abnormal fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week.

  • How they occur:
    • Complete mole Mole Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi: An enucleated ovum (i.e., an egg without any DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure) is fertilized by 1 sperm (that duplicates) or 2 sperm (rare).
    • Partial mole Mole Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi: 2 sperm fertilize a haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics ovum.
  • Ultrasound findings:
    • Enlarged uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy
    • Heterogeneous tissue within the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy with a classic “snowstorm” appearance
    • Fetus/fetal parts may or may not be present.
    • Large bilateral ovarian cysts Ovarian cysts Ovarian cysts are defined as collections of fluid or semiliquid material, often walled off by a membrane, located in the ovary. These cysts are broadly categorized as either functional or neoplastic. Neoplastic ovarian cysts are subcategorized as either benign or malignant. Ovarian Cysts may be present.
Transvaginal ultrasonography molar pregnancy obstertic imaging

Transvaginal ultrasonography showing a molar pregnancy: The pattern is described as a “cluster of grapes.”

Image: “Molar pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care” by Mikael Häggström. License: CC0 1.0

Retained products of conception:

After an abortion Abortion Expulsion of the product of fertilization before completing the term of gestation and without deliberate interference. Spontaneous Abortion (either spontaneous or induced), or postpartum after delivery of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity, tissue may be retained within the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy. This phenomenon is known as retained products of conception and can lead to hemorrhage and infection. Ultrasound findings include:

Transvaginal ultrasound demonstrates a heterogenous echogenic mass

A transvaginal ultrasound demonstrates a heterogeneous echogenic mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast in the endometrial cavity (black arrow), representing retained products of conception.

Image: “Gray-scale US demonstrates an echogenic mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast in the endometrial cavity (black arrow)” by Maureen P. Kohi et al AL Amyloidosis. License: CC BY 3.0

Fetal abnormalities

Nuchal translucency for aneuploidy screening Screening Preoperative Care:

An assessment of the nuchal translucency (or thickness of the nuchal fold at the back of the neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess) is a part of common aneuploidy screening tests Screening tests Screening tests are used to identify people in the early stages of a disease and enable early intervention with the goal of reducing morbidity and mortality. Epidemiological Values of Diagnostic Tests.

  • Measures the hypoechoic Hypoechoic A structure that produces a low-amplitude echo (darker grays) Ultrasound (Sonography) region between the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions and soft tissue Soft Tissue Soft Tissue Abscess behind the cervical spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy
  • A thickened nuchal fold increases the risk for:
    • Trisomy Trisomy The possession of a third chromosome of any one type in an otherwise diploid cell. Types of Mutations 21 (most common)
    • Trisomies 13 and 18
    • Turner syndrome Turner syndrome Turner syndrome is a genetic condition affecting women, in which 1 X chromosome is partly or completely missing. The classic result is the karyotype 45,XO with a female phenotype. Turner syndrome is associated with decreased sex hormone levels and is the most common cause of primary amenorrhea. Turner Syndrome
    • Major congenital Congenital Chorioretinitis heart disease
    • Hydrocephalus Hydrocephalus Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial. Subarachnoid Hemorrhage
  • > 100 different developmental and genetic syndromes have also been associated with an increased nuchal fold
Nuchal translucency measurements

Nuchal translucency (NT) measurements:
Figure (A) shows a normal fetus (looking up). Figure (B) shows a fetus with trisomy Trisomy The possession of a third chromosome of any one type in an otherwise diploid cell. Types of Mutations 21 (looking down), demonstrating increased NT thickness.

Image: “Nuchal translucency measurements” by Barati M et al AL Amyloidosis. License: CC BY 2.5

Congenital Congenital Chorioretinitis anomalies:

Almost any area of the body can develop incorrectly, leading to congenital Congenital Chorioretinitis anomalies. Many of them are visible on ultrasound. Some of the clinically important anomalies and their associated ultrasound findings include:

  • Cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) defects (most common, found in approximately 1% of births):
  • Neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defects (2nd most common):
    • Anencephaly Anencephaly A malformation of the nervous system caused by failure of the anterior neuropore to close. Infants are born with intact spinal cords, cerebellums, and brainstems, but lack formation of neural structures above this level. The skull is only partially formed but the eyes are usually normal. This condition may be associated with folate deficiency. Affected infants are only capable of primitive (brain stem) reflexes and usually do not survive for more than two weeks. Neural Tube Defects (most common neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defect): absence of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification
    • Cephalocele: cranial defects through which the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification or meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy herniate outside the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy
    • Spina bifida/ meningocele Meningocele A congenital or acquired protrusion of the meninges, unaccompanied by neural tissue, through a bony defect in the skull or vertebral column. Neural Tube Defects/myelomeningocele: protrusion of the spinal contents through bony defects in the spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy
  • Abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen defects:
    • Omphalocele Omphalocele Omphalocele is a congenital anterior abdominal wall defect in which the intestines are covered by peritoneum and amniotic membranes. The condition results from the failure of the midgut to return to the abdominal cavity by 10 weeks’ gestation. Omphalocele: Multiple bowel loops (+/- liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy) are seen herniating through a membrane-covered midline abdominal defect.
    • Gastroschisis Gastroschisis Gastroschisis is a congenital abdominal wall defect characterized by the complete lack of closure of the abdominal musculature. A portion of intestine does not return to the abdominal cavity, thereby remaining in its early embryonic herniated state but with no coverings. Gastroschisis: Bowel loops protrude outside the abdominal cavity without an overlying membrane, through a lateral abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen defect.

Intrauterine growth restriction (IUGR):

  • Abnormally low EFW on a growth scan
  • Typically defined as an EFW < 10th percentile for the estimated gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care

Hydrops fetalis Hydrops fetalis Abnormal accumulation of serous fluid in two or more fetal compartments, such as skin; pleura; pericardium; placenta; peritoneum; amniotic fluid. General fetal edema may be of non-immunologic origin, or of immunologic origin as in the case of erythroblastosis fetalis. Parvovirus B19:

  • Hydrops fetalis refers to abnormal fluid collections in ≥ 2 of the following fetal compartments:
    • Significant skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema (present in almost all hydropic infants) > 5 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma
    • Ascites Ascites Ascites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection). Ascites
    • Pleural effusions
    • Pericardial effusions
  • Other potential ultrasound findings:
    • Polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios
    • Increased nuchal translucency
    • Increased placental thickness
Ultrasound images of an infant with hydrops fetalis

Ultrasound images of an infant with hydrops fetalis Hydrops fetalis Abnormal accumulation of serous fluid in two or more fetal compartments, such as skin; pleura; pericardium; placenta; peritoneum; amniotic fluid. General fetal edema may be of non-immunologic origin, or of immunologic origin as in the case of erythroblastosis fetalis. Parvovirus B19:
Axial Axial Computed Tomography (CT) (A) and oblique sagittal Sagittal Computed Tomography (CT) (B) images showing fetal ascites Ascites Ascites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection). Ascites (short white arrow) and floating bowel loops (b); axial Axial Computed Tomography (CT) image of the fetal head (C) showing significant scalp edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema (long white arrow)

Image: “Ultrasound images of an infant with hydrops fetalis Hydrops fetalis Abnormal accumulation of serous fluid in two or more fetal compartments, such as skin; pleura; pericardium; placenta; peritoneum; amniotic fluid. General fetal edema may be of non-immunologic origin, or of immunologic origin as in the case of erythroblastosis fetalis. Parvovirus B19” by Afzal et al AL Amyloidosis. License: CC BY 3.0

Placental abnormalities Placental abnormalities Normal placental structure and function are essential for a healthy pregnancy. Some of the most common placental abnormalities include structural anomalies (such as a succenturiate lobe or velamentous cord insertion), implantation anomalies (such as placenta accreta and placenta previa), and functional anomalies (such as placental insufficiency). Placental Abnormalities

Abnormal placentation:

Abnormal placentation refers to abnormal implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity. Ultrasound findings may show an abnormal placental location, or show it invading into the uterine wall.

  • Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity previa: Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity covers the internal cervical os.
  • Low-lying placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity: Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity is within 2 cm of the internal cervical os.
  • PAS: Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity is abnormally adherent to the uterine wall.
    • Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity accreta (approximately 65%): Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity attaches directly to the myometrium due to the partial or total absence of the decidua basalis.
    • Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity increta (15%): Placental villi invade into the myometrium.
    • Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity percreta (approximately 20%): Placental villi penetrate through the entire myometrium and may invade other surrounding structures.
Types of abnormal placentation

Types of abnormal placentation

Image by Lecturio. License: CC BY-NC-SA 4.0

Placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage:

Placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage refers to the premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis separation of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity, leading to maternal-fetal hemorrhage. Ultrasound findings are usually only seen in large abruptions and may include:

  • Hyper- or iso-echoic retroplacental hematoma Hematoma A collection of blood outside the blood vessels. Hematoma can be localized in an organ, space, or tissue. Intussusception
  • Heterogeneity within the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity
  • Separation of placental edges from the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy
  • Placental thickening
Ultrasound acute placental abruption

Acute placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage:
Note the bulky heterogeneous placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity (arrows) in this hypertensive, 29-week gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care pregnant individual.

Image: “Acute placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage” by Kinare A. License: CC BY 2.0

Fluid abnormalities

Fluid assessment, at least with an SDP, should be part of every obstetric ultrasound. Fluid abnormalities include:

  • Polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios: too much fluid (SDP ≥ 8 cm or AFI ≥ 24 cm)
  • Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios: too little fluid (SDP < 2 cm or AFI ≤ 5 cm)
  • Anhydramnios Anhydramnios An extreme case of oligohydramnios with no measurable pockets of amniotic fluid present. Oligohydramnios: no fluid (no measurable pockets of fluid)
Fetal environment - measuring single vertical pocket of liquor

Single deepest vertical pocket of fluid is measured using ultrasound to assess amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume. Polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios is present in this case (SDP > 8 cm).

Image: “Demonstration of the technique to measure a single vertical pocket of liquor” by Kinare A. License: CC BY 2.0

Other Imaging Modalities in Pregnancy

Nonsonographic obstetric imaging

Obstetric imaging outside of ultrasound is of limited utility and confined to very specific indications.

  • MRI may be used for:
    • Evaluation of specific fetal congenital Congenital Chorioretinitis abnormalities noted on ultrasound
    • Characterization of maternal pelvic anatomy in cases with unusual or complex abnormalities
  • CT is almost never indicated for evaluation of the fetus or maternal pelvic anatomy for obstetric indications.
Mri findings fetal chiari ii malformation

Magnetic resonance imaging findings in a fetus at 23 wga, suggestive of a fetal Chiari II malformation:
a: T2-weighted sagittal Sagittal Computed Tomography (CT) image demonstrating a lumbosacral neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defect (encircled) with cerebellar tonsillar herniation Herniation Omphalocele (arrow)
b: T2-weighted sagittal Sagittal Computed Tomography (CT) image demonstrating a myelomeningocele (encircled) from L2 to the end of the sacrum Sacrum Five fused vertebrae forming a triangle-shaped structure at the back of the pelvis. It articulates superiorly with the lumbar vertebrae, inferiorly with the coccyx, and anteriorly with the ilium of the pelvis. The sacrum strengthens and stabilizes the pelvis. Vertebral Column: Anatomy
c: T2-weighted axial Axial Computed Tomography (CT) image showing the myelomeningocele (encircled)
d: T2-weighted axial Axial Computed Tomography (CT) image demonstrating hydrocephalus Hydrocephalus Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial. Subarachnoid Hemorrhage

Image: “ Neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defect with tonsillar herniation Herniation Omphalocele” by Loomba R. License: CC BY 3.0

Nonobstetric imaging during pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care

  • Ultrasound and MRI are the preferred modalities due to the lack of radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma exposure Exposure ABCDE Assessment.
    • Example: Abdominal ultrasound is the preferred initial test for appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis over CT.
  • Chest X-ray Chest X-ray X-ray visualization of the chest and organs of the thoracic cavity. It is not restricted to visualization of the lungs. Pulmonary Function Tests:
    • Abdomen should be shielded.
    • Only done when absolutely necessary (e.g., clinical deterioration with concern for pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia).
    • Indicated in cases of choriocarcinoma Choriocarcinoma A malignant metastatic form of trophoblastic tumors. Unlike the hydatidiform mole, choriocarcinoma contains no chorionic villi but rather sheets of undifferentiated cytotrophoblasts and syncytiotrophoblasts (trophoblasts). It is characterized by the large amounts of chorionic gonadotropin produced. Tissue origins can be determined by DNA analyses: placental (fetal) origin or non-placental origin. Gestational Trophoblastic Disease to evaluate for lung metastases
  • If CT is the modality required to make an important diagnosis (e.g., an individual presenting with stroke symptoms):
    • A single CT scan in pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care is considered relatively safe.
    • Risks/benefits should be carefully weighed and discussed with the individual.
X-ray round left midlung airspace opacity

Round, left midlung airspace opacity Opacity Imaging of the Lungs and Pleura in an individual reported to have gestational trophoblastic disease Gestational trophoblastic disease Gestational trophoblastic diseases are a spectrum of placental disorders resulting from abnormal placental trophoblastic growth. These disorders range from benign molar pregnancies (complete and partial moles) to neoplastic conditions such as invasive moles and choriocarcinoma. Gestational Trophoblastic Disease

Image: “The appearance of lung metastasis Metastasis The transfer of a neoplasm from one organ or part of the body to another remote from the primary site. Grading, Staging, and Metastasis in patient that was reported” by Ghaemmaghami F. License: CC BY 2.5

Clinical Relevance

Obstetric imaging is a critical part of almost all obstetric care.

Diagnosing abnormal pregnancies

  • Ectopic pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care: pregnancies that have implanted outside the uterine cavity, most commonly in the fallopian tubes Fallopian tubes The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The fallopian tubes receive an ovum after ovulation and help move it and/or a fertilized embryo toward the uterus via ciliated cells lining the tubes and peristaltic movements of its smooth muscle. Uterus, Cervix, and Fallopian Tubes: Anatomy. Ectopic pregnancies are nonviable and may rupture as they grow, leading to life-threatening maternal hemorrhage. Individuals typically present with lower abdominal pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways and/or abnormal bleeding; a urine Urine Liquid by-product of excretion produced in the kidneys, temporarily stored in the bladder until discharge through the urethra. Bowen Disease and Erythroplasia of Queyrat pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care test will be positive. Management is either with methotrexate Methotrexate An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of tetrahydrofolate dehydrogenase and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA. Antimetabolite Chemotherapy or surgical excision, depending on the case.
  • Molar pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care: arises from abnormal fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week, resulting in abnormal embryonic genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics. The classic clinical presentation Presentation The position or orientation of the fetus at near term or during obstetric labor, determined by its relation to the spine of the mother and the birth canal. The normal position is a vertical, cephalic presentation with the fetal vertex flexed on the neck. Normal and Abnormal Labor is hyperemesis (severe nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics and vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia), 1st trimester vaginal bleeding, and enlarged uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy relative to the individual’s estimated gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care. Diagnosis is by ultrasound and abnormally elevated hCG levels. Suction and curettage Curettage A scraping, usually of the interior of a cavity or tract, for removal of new growth or other abnormal tissue, or to obtain material for tissue diagnosis. It is performed with a curet (curette), a spoon-shaped instrument designed for that purpose. Benign Bone Tumors are the mainstays of treatment and post-procedural monitoring is essential to ensure that invasive disease does not develop.
Table: Characteristics of complete versus partial molar pregnancies
Complete mole Mole Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi Partial mole Mole Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi
Karyotype Karyotype The full set of chromosomes presented as a systematized array of metaphase chromosomes from a photomicrograph of a single cell nucleus arranged in pairs in descending order of size and according to the position of the centromere. Congenital Malformations of the Female Reproductive System 46,XX or 46,XY Triploid (69,XXX, 69, XXY XXY Klinefelter syndrome is a chromosomal aneuploidy characterized by the presence of 1 or more extra X chromosomes in a male karyotype, most commonly leading to karyotype 47,XXY. Klinefelter syndrome is associated with decreased levels of testosterone and is the most common cause of congenital hypogonadism. Klinefelter Syndrome, or 69,XYY)
Formed from Enucleated egg and a single sperm 2 sperm and 1 egg
Fetal parts Absent Present
Human chorionic gonadotropin levels ↑↑↑
Ultrasound findings
  • Honeycomb uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy
  • “Clusters of grapes”
  • “Snowstorm” uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy
Reveals fetal parts
Malignancy Malignancy Hemothorax risk Higher risk for choriocarcinoma Choriocarcinoma A malignant metastatic form of trophoblastic tumors. Unlike the hydatidiform mole, choriocarcinoma contains no chorionic villi but rather sheets of undifferentiated cytotrophoblasts and syncytiotrophoblasts (trophoblasts). It is characterized by the large amounts of chorionic gonadotropin produced. Tissue origins can be determined by DNA analyses: placental (fetal) origin or non-placental origin. Gestational Trophoblastic Disease Rare

Fetal issues

  • Fetal anomalies: abnormalities in the fetus due to either genetic, chromosomal, or developmental abnormalities. Fetal anomalies can occur in any organ system throughout the body; clinical presentation Presentation The position or orientation of the fetus at near term or during obstetric labor, determined by its relation to the spine of the mother and the birth canal. The normal position is a vertical, cephalic presentation with the fetal vertex flexed on the neck. Normal and Abnormal Labor and management will depend on the specific anomalies. The most common are cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) and neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defects.
  • Fetal growth restriction Fetal growth restriction Fetal growth restriction (FGR), also known as intrauterine fetal growth restriction (IUGR), is an estimated fetal weight (EFW) or abdominal circumference < 10th percentile for gestational age. The term small for gestational age (SGA) is sometimes erroneously used interchangeably with FGR. Fetal Growth Restriction ( FGR FGR Fetal growth restriction (FGR), also known as intrauterine fetal growth restriction (IUGR), is an estimated fetal weight (EFW) or abdominal circumference < 10th percentile for gestational age. The term small for gestational age (sga) is sometimes erroneously used interchangeably with FGR. Fetal Growth Restriction): a condition, also known as IUGR, referring to poor fetal growth in utero due to environmental factors. Fetal growth restriction Fetal growth restriction Fetal growth restriction (FGR), also known as intrauterine fetal growth restriction (IUGR), is an estimated fetal weight (EFW) or abdominal circumference < 10th percentile for gestational age. The term small for gestational age (SGA) is sometimes erroneously used interchangeably with FGR. Fetal Growth Restriction is typically defined as an EFW < the 10th percentile based on the estimated gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care. The primary pathogenesis is due to poor perfusion through the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity, limiting the oxygen and nutrients available to the fetus. There are numerous fetal, maternal, and placental etiologies.
  • Hydrops fetalis Hydrops fetalis Abnormal accumulation of serous fluid in two or more fetal compartments, such as skin; pleura; pericardium; placenta; peritoneum; amniotic fluid. General fetal edema may be of non-immunologic origin, or of immunologic origin as in the case of erythroblastosis fetalis. Parvovirus B19: an abnormal collection of fluid within the fetus. Diagnosis requires at least 2 of the following (all visible on obstetric ultrasound) presentations: skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema, ascites Ascites Ascites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection). Ascites, pleural effusions, or pericardial effusions. Hydrops fetalis Hydrops fetalis Abnormal accumulation of serous fluid in two or more fetal compartments, such as skin; pleura; pericardium; placenta; peritoneum; amniotic fluid. General fetal edema may be of non-immunologic origin, or of immunologic origin as in the case of erythroblastosis fetalis. Parvovirus B19 is often caused by maternal antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions against fetal RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology leading to severe fetal anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types, although there are several nonimmune etiologies as well (e.g., infection with parvovirus B19 Parvovirus B19 Primate erythroparvovirus 1 (generally referred to as parvovirus B19, B19 virus, or sometimes erythrovirus B19) ranks among the smallest DNA viruses. Parvovirus B19 is of the family Parvoviridae and genus Erythrovirus. In immunocompetent humans, parvovirus B19 classically results in erythema infectiosum (5th disease) or “slapped cheek syndrome.” Parvovirus B19). Often, the primary management is close monitoring, with induced preterm delivery when fetal status begins to deteriorate.

Abnormal placentation

  • Placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity previa: the presence of placental tissue covering the internal cervical os. When the cervix Cervix The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Externally, the cervix is lined by stratified squamous cells; however, the cervical canal is lined by columnar epithelium. Uterus, Cervix, and Fallopian Tubes: Anatomy begins dilating, the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity will become “detached” over the opening cervical os, resulting in life-threatening maternal-fetal hemorrhage. Diagnosis is using obstetric ultrasound (usually transvaginal). Management is by avoiding any digital cervical exams and delivering the infant via cesarean delivery Cesarean Delivery Cesarean delivery (CD) is the operative delivery of ≥ 1 infants through a surgical incision in the maternal abdomen and uterus. Cesarean deliveries may be indicated for a number of either maternal or fetal reasons, most commonly including fetal intolerance to labor, arrest of labor, a history of prior uterine surgery, fetal malpresentation, and placental abnormalities. Cesarean Delivery prior to the onset of labor Labor Labor is the normal physiologic process defined as uterine contractions resulting in dilatation and effacement of the cervix, which culminates in expulsion of the fetus and the products of conception. Normal and Abnormal Labor.
  • PAS: describes a spectrum in which the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity is abnormally and firmly adherent to the uterine wall. In this situation, the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity is unable to detach postpartum and continues to bleed, often heavily, resulting in life-threatening hemorrhage. The 3 degrees of PAS are placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity accreta, increta, and percreta. Diagnosis is via ultrasound, and management is usually surgical, often including a planned hysterectomy at the time of cesarean delivery Cesarean Delivery Cesarean delivery (CD) is the operative delivery of ≥ 1 infants through a surgical incision in the maternal abdomen and uterus. Cesarean deliveries may be indicated for a number of either maternal or fetal reasons, most commonly including fetal intolerance to labor, arrest of labor, a history of prior uterine surgery, fetal malpresentation, and placental abnormalities. Cesarean Delivery.

Abnormal amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volumes

  • Polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios: a pathological excess of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity. Common causes include fetal anomalies, gestational diabetes Gestational diabetes Diabetes mellitus induced by pregnancy but resolved at the end of pregnancy. It does not include previously diagnosed diabetics who become pregnant (pregnancy in diabetics). Gestational diabetes usually develops in late pregnancy when insulin antagonistic hormones peaks leading to insulin resistance; glucose intolerance; and hyperglycemia. Diabetes Mellitus, multiple gestations, and congenital Congenital Chorioretinitis infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease. Diagnosis is made based on ultrasound with an AFI ≥ 24 cm or an SDP ≥ 8 cm. Management of moderate-to-severe cases includes amnioreduction Amnioreduction Polyhydramnios, medical therapy, and careful management during labor Labor Labor is the normal physiologic process defined as uterine contractions resulting in dilatation and effacement of the cervix, which culminates in expulsion of the fetus and the products of conception. Normal and Abnormal Labor. Major risks include cord prolapse and placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage at the time of membrane rupture.
  • Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios: a condition characterized by pathologically low amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volumes. Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios is diagnosed by ultrasound and defined as an AFI of ≤ 5 cm or an SDP of < 2 cm in the 2nd and 3rd trimesters. Etiologies include uteroplacental insufficiency Uteroplacental Insufficiency Uteroplacental insufficiency may be acute or chronic and refers to the inability of the placenta to deliver a sufficient supply of O2 and nutrients to the fetus Placental Abnormalities, drugs, fetal malformations (especially those related to renal/urinary systems), and maternal TORCH infections TORCH infections Congenital infections are acquired in utero or during passage through the birth canal at birth and can be associated with significant morbidity and mortality for the infant. The TORCH infections are a group of congenital infections grouped due to their similar presentation. The acronym TORCH arises from the names of the infectious agents that cause the diseases included in this group: toxoplasmosis, other agents (syphilis, varicella zoster virus (VZV), parvovirus B19, and HIV), rubella, CMV, and herpes simplex. Congenital TORCH Infections. Management involves close antenatal monitoring because significant complications are possible, including FGR FGR Fetal growth restriction (FGR), also known as intrauterine fetal growth restriction (IUGR), is an estimated fetal weight (EFW) or abdominal circumference < 10th percentile for gestational age. The term small for gestational age (sga) is sometimes erroneously used interchangeably with FGR. Fetal Growth Restriction, preterm delivery, and developmental deformities.

References

  1. Shipp, T.D. (2021). Overview of ultrasound examination in obstetric and gynecology. In Barss, V.A. (Ed.), UpToDate. Retrieved July 30, 2021, from https://www.uptodate.com/contents/overview-of-ultrasound-examination-in-obstetrics-and-gynecology 
  2. Magann, E., Ross, M.G. (2021). Assessment of amniotic fluid volume. In Barss, V.A., (Ed.), UpToDate. Retrieved July 30, 2021, from https://www.uptodate.com/contents/assessment-of-amniotic-fluid-volume 
  3. Berkowitz, R.S., et al. (2020). Hydatidiform mole: Epidemiology, clinical features, and diagnosis. UpToDate. Retrieved July 30, 2021, from https://www.uptodate.com/contents/hydatidiform-mole-epidemiology-clinical-features-and-diagnosis
  4. Weeks, A. (2021). Retained placenta after vaginal birth. UpToDate. Retrieved July 30, 2021, from https://www.uptodate.com/contents/retained-placenta-after-vaginal-birth

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