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Placenta, Umbilical Cord, and Amniotic Cavity

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, fetal development and growth are sustained completely by the mother until birth. The placenta consists of a fetal side and a maternal side, and it provides a vascular communication Communication The exchange or transmission of ideas, attitudes, or beliefs between individuals or groups. Decision-making Capacity and Legal Competence between the mother and the fetus. This communication Communication The exchange or transmission of ideas, attitudes, or beliefs between individuals or groups. Decision-making Capacity and Legal Competence allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. The placenta is also called “the fetal lung” because it allows for gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange between the maternal and fetal circulation Fetal circulation Prenatal and Postnatal Physiology of the Neonate. Diseases or defects in the placenta often have severe, and even fatal, complications.

Last updated: Jun 9, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Placental Structure, Circulation, and Function

Placental structure

The placenta has a pancake-like appearance, with 2 sides: 

  • Placenta:
    • Basal plate Basal plate Development of the Nervous System and Face (maternal side): 
      • Divided into lobes 
      • Separated by septa
    • Chorionic plate (fetal side): 
      • Contains branching chorionic villi, providing a massive surface for exchange
      • Umbilical cord emerges from the fetal side of the placenta.
  • Membranes (by delivery they have fused into a single membrane):
    • Amnion
    • Chorion
  • Umbilical cord:
    • 2 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: carry deoxygenated fetal blood to the placenta
    • 1 vein: carries oxygenated blood back to the fetus
Placenta maternal and fetal side

2 placentas:
Left: Maternal side
Right: Fetal side

Image: “PlacentaPair” by Albert Cahalan. License: Public Domain

Placental circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment

  • Chorionic villi provide a large surface area for maternal–fetal exchange.
  • Spiral Spiral Computed tomography where there is continuous x-ray exposure to the patient while being transported in a spiral or helical pattern through the beam of irradiation. This provides improved three-dimensional contrast and spatial resolution compared to conventional computed tomography, where data is obtained and computed from individual sequential exposures. Computed Tomography (CT) 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 (maternal) fill the intervillous spaces in the decidua basalis layer of the 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:
    • Bring in oxygenated blood for fetus
    • These spiral Spiral Computed tomography where there is continuous x-ray exposure to the patient while being transported in a spiral or helical pattern through the beam of irradiation. This provides improved three-dimensional contrast and spatial resolution compared to conventional computed tomography, where data is obtained and computed from individual sequential exposures. Computed Tomography (CT) 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 “rupture” and become large spaces called lacunae Lacunae Bones: Development and Ossification, which:
  • 2 umbilical 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 bring deoxygenated blood from fetus to placental chorionic villi
  • Gas and molecule exchange occurs between the fetal blood in the chorionic villi and the maternal blood in the lacunae Lacunae Bones: Development and Ossification, across the placental barrier (see below for layers).
  • 1 umbilical vein umbilical vein Venous vessels in the umbilical cord. They carry oxygenated, nutrient-rich blood from the mother to the fetus via the placenta. In humans, there is normally one umbilical vein. Prenatal and Postnatal Physiology of the Neonate transports oxygenated blood back to the fetus.
  • Maternal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology take deoxygenated blood back to the maternal circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment.
  • Maternal and fetal blood never come into direct contact.
  • Fetal hemoglobin has ↑ affinity for oxygen compared to maternal hemoglobin → causes O2 to move from maternal 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 to 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.
Placental circulation

Diagram of placental circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment

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

Placental barrier

The placental barrier is a selectively permeable membrane separating the maternal and fetal blood. The barrier is comprised of the following layers:

The placental barrier

Circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment within chorionic villi and the components of the placental barrier

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

Functions of the placenta

The table lists the many critical functions of the placenta for the fetus.

Table: Functions of the placenta
Primary functions Important details
Gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange
  • O2–CO2 exchange
  • Occurs via simple diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis
Nutrient exchange
  • Provides materials needed for fetal development and growth
  • Mechanisms of exchange:
    • Water and sodium Sodium A member of the alkali group of metals. It has the atomic symbol na, atomic number 11, and atomic weight 23. Hyponatremia by simple diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis
    • Glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance by facilitated diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis
    • Large molecules (e.g., LDLs, peptides, 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) by receptor-mediated endocytosis Endocytosis Cellular uptake of extracellular materials within membrane-limited vacuoles or microvesicles. Endosomes play a central role in endocytosis. The Cell: Cell Membrane
    • Amino acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance by secondary active transport Active transport The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy. The Cell: Cell Membrane
Waste product Product A molecule created by the enzymatic reaction. Basics of Enzymes removal
  • Waste products (e.g., urea Urea A compound formed in the liver from ammonia produced by the deamination of amino acids. It is the principal end product of protein catabolism and constitutes about one half of the total urinary solids. Urea Cycle and CO2) are transported back to the mother.
  • Occurs via simple diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis
Hormonal secretion Secretion Coagulation Studies
  • hCG: maintains the activity of the corpus luteum Corpus Luteum The yellow body derived from the ruptured ovarian follicle after ovulation. The process of corpus luteum formation, luteinization, is regulated by luteinizing hormone. Ovaries: Anatomy required for continuation 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
  • Human growth hormone Human growth hormone A 191-amino acid polypeptide hormone secreted by the human adenohypophysis, also known as gh or somatotropin. Synthetic growth hormone, termed somatropin, has replaced the natural form in therapeutic usage such as treatment of dwarfism in children with growth hormone deficiency. Idiopathic Intracranial Hypertension ( hGH HGH A 191-amino acid polypeptide hormone secreted by the human adenohypophysis, also known as gh or somatotropin. Synthetic growth hormone, termed somatropin, has replaced the natural form in therapeutic usage such as treatment of dwarfism in children with growth hormone deficiency. Idiopathic Intracranial Hypertension)
  • Human placental lactogen: stimulates maternal insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin production to ↑ glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance available to the fetus
  • Chorionic thyrotropin
  • Chorionic corticotropin-releasing hormone Corticotropin-releasing hormone A peptide of about 41 amino acids that stimulates the release of adrenocorticotropic hormone. Crh is synthesized by neurons in the paraventricular nucleus of the hypothalamus. After being released into the pituitary portal circulation, crh stimulates the release of acth from the pituitary gland. Crh can also be synthesized in other tissues, such as placenta; adrenal medulla; and testis. Hypothalamic and Pituitary Hormones (CRH)
  • 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: maintains 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, prevents menstruation Menstruation The periodic shedding of the endometrium and associated menstrual bleeding in the menstrual cycle of humans and primates. Menstruation is due to the decline in circulating progesterone, and occurs at the late luteal phase when luteolysis of the corpus luteum takes place. Menstrual Cycle
  • Estrogens
  • Glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids
Metabolic functions
Immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs rejection Creation of an immunologically privileged site
Transport across the placental barrier diagram

Transport across the placental barrier

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

Placental Development

Steps in placental development: 

  • Implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week begins 7–9 days after 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.
  • Fetal cells involved in placental formation:
    • Cytotrophoblast Cytotrophoblast Embryoblast and Trophoblast Development: the outer layer of cells of the blastocyst Blastocyst A post-morula preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper. Fertilization and First Week
    • Syncytiotrophoblast Syncytiotrophoblast Embryoblast and Trophoblast Development
      • Outer layer of cells of the blastocyst Blastocyst A post-morula preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper. Fertilization and First Week in contact with the uterine wall
      • Invade uterine wall
      • Have lost their outer membranes and are simply “nuclei” floating in cytoplasm, eating their way into the uterine wall
  • Trophoblastic villi begin to form from invaginations of cytotrophoblast Cytotrophoblast Embryoblast and Trophoblast Development into the space created by the syncytiotrophoblast Syncytiotrophoblast Embryoblast and Trophoblast Development.
  • On the maternal side, lacunae Lacunae Bones: Development and Ossification are created from ruptured maternal blood vessels in the decidua basalis layer of the 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:
  • The trophoblastic villi begin creating a branching tree-like structure for nutrient and gas exchange Gas exchange Human cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood. Gas Exchange:
  • These vessels ultimately connect to fetal umbilical vessels, later forming the umbilical cord. 
  • Villi become increasingly more concentrated opposite to the endometrial cavity, forming the chorion frondosum.

Umbilical Cord

Definition

The umbilical cord connects the fetus to the placenta. The cord contains 2 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 and 1 vein and extends from the fetal umbilicus to the fetal surface of the placenta.

Umbilical cord structure

  • Vessels: 
    • Contains 2 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 and 1 vein
    • Vessels are surrounded by a protective substance called Wharton’s jelly.
    • Counted by sonographic evaluation, with the 3 vessels seen in the 1st trimester
    • Coiling: The vein and 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 spiral Spiral Computed tomography where there is continuous x-ray exposure to the patient while being transported in a spiral or helical pattern through the beam of irradiation. This provides improved three-dimensional contrast and spatial resolution compared to conventional computed tomography, where data is obtained and computed from individual sequential exposures. Computed Tomography (CT) around each other.
  • Blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure:
    • Umbilical vein umbilical vein Venous vessels in the umbilical cord. They carry oxygenated, nutrient-rich blood from the mother to the fetus via the placenta. In humans, there is normally one umbilical vein. Prenatal and Postnatal Physiology of the Neonate supplies oxygenated blood to the fetus.
    • Umbilical 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 take deoxygenated blood away from the fetus.
  • Cord length:
  • Insertion into the placenta:
    • Normal: central insertion
    • Variants: 
      • Eccentric, marginal: the cord inserts on the edge of the placenta.
      • Velamentous: occurs when the last portion of the umbilical cord lacks the protective Wharton’s jelly, leaving the umbilical vessels exposed
    • Clinical relevance of abnormal insertion: may increase the risk of complications 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 and/or delivery, like umbilical cord rupture and/or antenatal hemorrhage
Cross section of the human umbilical cord

Cross section of the human umbilical cord
A: Artery
V: Vein
WJ: Wharton’s jelly

Image: “Cross-section of the human umbilical cord” by Irina Arutyunyan, et al AL Amyloidosis. License: CC BY 4.0, cropped by Lecturio.

Amniotic Cavity

The amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development is a fluid-filled cavity that encases the developing 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/fetus; the fluid is called amniotic fluid.

  • Development: the amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development appears on day 8 of gestation as amniotic fluid collects between cells of the epiblast Epiblast Embryoblast and Trophoblast Development and trophoblast Trophoblast Cells lining the outside of the blastocyst. After binding to the endometrium, trophoblasts develop into two distinct layers, an inner layer of mononuclear cytotrophoblasts and an outer layer of continuous multinuclear cytoplasm, the syncytiotrophoblasts, which form the early fetal-maternal interface (placenta). Fertilization and First Week.
  • Amnion:
  • Functions of the amnion:
    • Involved in solute and water transport required for amniotic fluid homeostasis Homeostasis The processes whereby the internal environment of an organism tends to remain balanced and stable. Cell Injury and Death
    • Produces bioactive compounds
  • Amniotic fluid: 
    • Liquid that surrounds the 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 and fetus during its development
    • As the fetus grows, it “creates” amniotic fluid via urination, and continually “recycles” the fluid by swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility it.
    • Congenital Congenital Chorioretinitis defects in swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility and/or the renal/urinary system can lead to abnormalities in amniotic fluid volume.
  • Functions of the amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development:
    • Protects fetus against trauma
    • Protects umbilical cord against compression Compression Blunt Chest Trauma
    • Nutrient reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli for the fetus
    • Provides adequate space for normal fetal growth and development (especially the limbs and 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)

Placenta and Childbirth

  • The delivery of the placenta constitutes the 3rd stage 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.
  • As the newborn Newborn An infant during the first 28 days after birth. Physical Examination of the Newborn is delivered, the uterine cavity undergoes contraction, causing separation of the placenta.
  • As separation begins, a hematoma Hematoma A collection of blood outside the blood vessels. Hematoma can be localized in an organ, space, or tissue. Intussusception is formed between the uterine decidua and the placenta → detaches it from the uterine wall
  • Once completely loose, the placenta is removed through the birth canal Birth canal Pelvis: Anatomy, which can occur via:
    • Passive management: Natural uterine contractions expel the placenta.
    • Active management: provider applies gentle downward traction on the clamped umbilical cord while providing countertraction with firm suprapubic pressure:
      • Avoid downward fundal pressure during placental delivery, which can lead to uterine inversions.
      • Gentle downward traction prevents tearing of the umbilical cord.
      • Active management is usually recommended to reduce hemorrhage risk.
  • Signs the placenta is ready to deliver:
    • Lengthening of the umbilical cord
    • Gush of blood
    • 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 becomes more globular.
Placenta delivery

Delivery of the placenta via gentle downward traction on the umbilical cord and countertraction on 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:
Note that the umbilical cord is not clamped in this example.

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

Clinical Relevance

  • Placenta previa Placenta Previa Abnormal placentation in which the placenta implants in the lower segment of the uterus (the zone of dilation) and may cover part or all of the opening of the cervix. It is often associated with serious antepartum bleeding and premature labor. Placental Abnormalities: abnormal attachment Attachment The binding of virus particles to virus receptors on the host cell surface, facilitating virus entry into the cell. Virology of the placenta in the lower uterine segment, which can obstruct (partially or completely) the internal cervical os. Maternal and fetal hemorrhage can result from cervical dilation Cervical dilation A measurement of the diameter of the cervical canal, reported in centimeters Normal and Abnormal Labor. Placenta previa Placenta Previa Abnormal placentation in which the placenta implants in the lower segment of the uterus (the zone of dilation) and may cover part or all of the opening of the cervix. It is often associated with serious antepartum bleeding and premature labor. Placental Abnormalities classically presents as painless bright red vaginal bleeding and is diagnosed by ultrasonography. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship are treated with pelvic rest (avoiding digital exams and intercourse) and are delivered 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 (CD) 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 (or emergently if there is clinical bleeding).
  • Vasa previa Vasa previa Pregnancy complication where fetal blood vessels, normally inside the umbilical cord, are left unprotected and cross fetal membranes. It is associated with antepartum bleeding and fetal death and stillbirth due to exsanguination. Antepartum Hemorrhage: situation in which the vessels of the umbilical cord traverse the internal cervical os. Often these vessels are not surrounded by the protective Wharton’s jelly ( velamentous cord insertion Velamentous cord insertion The last few centimeters of the umbilical cord entering the placenta lack the protective Wharton’s jelly. The vessels are “exposed” and covered only by the fetal membranes Placental Abnormalities) and can rupture easily, leading to maternal and fetal hemorrhage. Vasa previa Vasa previa Pregnancy complication where fetal blood vessels, normally inside the umbilical cord, are left unprotected and cross fetal membranes. It is associated with antepartum bleeding and fetal death and stillbirth due to exsanguination. Antepartum Hemorrhage is diagnosed with ultrasonography. The potential for vasa previa Vasa previa Pregnancy complication where fetal blood vessels, normally inside the umbilical cord, are left unprotected and cross fetal membranes. It is associated with antepartum bleeding and fetal death and stillbirth due to exsanguination. Antepartum Hemorrhage (and/or placenta previa Placenta Previa Abnormal placentation in which the placenta implants in the lower segment of the uterus (the zone of dilation) and may cover part or all of the opening of the cervix. It is often associated with serious antepartum bleeding and premature labor. Placental Abnormalities) is the primary reason why it is imperative to know the location of the placenta prior to performing a digital cervical exam. These infants must be delivered via CD 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.
  • Placenta accreta Placenta Accreta Abnormal placentation in which all or parts of the placenta are attached directly to the myometrium due to a complete or partial absence of decidua. It is associated with postpartum hemorrhage because of the failure of placental separation. Placental Abnormalities, placenta increta, and placenta percreta: abnormal implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week of the placenta into the uterine wall. In placenta accreta Placenta Accreta Abnormal placentation in which all or parts of the placenta are attached directly to the myometrium due to a complete or partial absence of decidua. It is associated with postpartum hemorrhage because of the failure of placental separation. Placental Abnormalities, villi invade to the myometrium. In placenta increta, villi penetrate deeper into the myometrium. In placenta percreta, villi reach the uterine serosa and/or invade other organs. These conditions are diagnosed by ultrasonography. Women with these conditions are delivered via planned CD, often with concurrent hysterectomy (especially in cases of increta and percreta because full removal of the placenta, and thus cessation of hemorrhage, may be impossible).
  • 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 (partial or complete) of the placenta from the uterine wall before delivery of the infant. Abruption is primarily a clinical diagnosis based on a presentation with painful contractions with or without bleeding (look for a history of trauma or other risk factors) with characteristic findings on fetal monitoring Fetal monitoring The primary goals of antepartum testing and monitoring are to assess fetal well-being, identify treatable situations that may cause complications, and evaluate for chromosomal abnormalities. These tests are divided into screening tests (which include cell-free DNA testing, serum analyte testing, and nuchal translucency measurements), and diagnostic tests, which provide a definitive diagnosis of aneuploidy and include chorionic villus sampling (CVS) and amniocentesis. Antepartum Testing and Monitoring and tocometry. Large abruptions may be seen on ultrasonography, but smaller ones frequently are not. Management depends on 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 size of abruption; significant abruptions require immediate delivery.
  • Hydatidiform moles Moles Primary Skin Lesions: spectrum of placental disorders resulting from abnormal placental trophoblastic growth. Hydatidiform moles Moles Primary Skin Lesions range from benign Benign Fibroadenoma molar pregnancies to neoplastic conditions discovered postpartum, such as 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. Diagnosis is confirmed by high serum β-hCG levels and characteristic ultrasound findings. Management is primarily through dilation 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 and/or 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
  • 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: excess amniotic fluid, diagnosed on ultrasonography. 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 may lead to an increased risk of preterm labor Preterm labor Preterm labor refers to regular uterine contractions leading to cervical change prior to 37 weeks of gestation; preterm birth refers to birth prior to 37 weeks of gestation. Preterm birth may be spontaneous due to preterm labor, preterm prelabor rupture of membranes (PPROM), or cervical insufficiency. Preterm Labor and Birth, 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 rupture of membranes, umbilical cord prolapse (when membranes rupture), 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, and fetal malpresentation Fetal malpresentation Any presentation other than vertex. Clinically, this means breech, face, brow, and shoulder presentations Fetal Malpresentation and Malposition (e.g., breech). Most mild cases are idiopathic Idiopathic Dermatomyositis or associated with maternal diabetes Diabetes Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus; however, other causes may include obstruction in the fetal GI tract (e.g., esophageal atresia Esophageal atresia Esophageal atresia is a congenital anomaly in which the upper esophagus is separated from the lower esophagus and ends in a blind pouch. The condition may be isolated or associated with tracheoesophageal fistula, which is an abnormal connection between the trachea and esophagus. Esophageal Atresia and Tracheoesophageal Fistula), neuromuscular disorders that affect Affect The feeling-tone accompaniment of an idea or mental representation. It is the most direct psychic derivative of instinct and the psychic representative of the various bodily changes by means of which instincts manifest themselves. Psychiatric Assessment swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility, aneuploidy, or high cardiac output Cardiac output The volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat). Cardiac Mechanics states (e.g., arteriovenous shunting).
  • 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: low levels of amniotic fluid, diagnosed on ultrasonography. Causes of 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 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 (e.g., 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), medications (e.g., ACEis ACEIs A class of drugs whose main indications are the treatment of hypertension and heart failure. They exert their hemodynamic effect mainly by inhibiting the renin-angiotensin system. They also modulate sympathetic nervous system activity and increase prostaglandin synthesis. They cause mainly vasodilation and mild natriuresis without affecting heart rate and contractility. Heart Failure and Angina Medication), placental thrombosis Thrombosis Formation and development of a thrombus or blood clot in the blood vessel. Epidemic Typhus, 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, and congenital Congenital Chorioretinitis anomalies associated with urine production. Many cases are due to poor circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment through the placenta, which increases the risk of poor fetal lung, 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, and musculoskeletal development, preterm birth Preterm birth Preterm labor refers to regular uterine contractions leading to cervical change prior to 37 weeks of gestation; preterm birth refers to birth prior to 37 weeks of gestation. Preterm birth may be spontaneous due to preterm labor, preterm prelabor rupture of membranes (PPROM), or cervical insufficiency. Preterm Labor and Birth, and other 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 complications.

References

  1. Cunningham, F. G., Leveno, K. J., Bloom, S. L., Dashe, J. S., Hoffman, B. L., Casey, B. M., Spong, C. Y. (2018). Physiology of labor. In: Williams Obstetrics, 25th ed. New York: McGraw-Hill Education.
  2. Cunningham, F. G., Leveno, K. J., Bloom, S. L., Dashe, J. S., Hoffman, B. L., Casey, B. M., Spong, C. Y. (2018). Implantation and placental development. In: Williams Obstetrics, 25th ed. New York: McGraw-Hill Education.
  3. Cunningham, F. G., Leveno, K. J., Bloom, S. L., Dashe, J. S., Hoffman, B. L., Casey, B. M., & Spong, C. Y. (2018). Placental abnormalities. In: Williams Obstetrics, 25th ed. New York: McGraw-Hill Education.
  4. Kibble, J. D., Halsey, C. R. (2015). Reproductive physiology. In: Medical physiology: the big picture. New York: McGraw-Hill Education.
  5. Paulsen, D. F. (2010). Female reproductive system. Chapter 23 of Histology & Cell Biology: Examination & Board Review, 5th ed. New York: McGraw-Hill.
  6. Flick, A. A., Kahn, D. A. (2013). Maternal physiology during pregnancy & fetal & early neonatal physiology. Chapter 8 of DeCherney, A. H., Nathan, L., Laufer, N., Roman, A. S. (Eds.), Current Diagnosis & Treatment: Obstetrics & Gynecology, 11th ed. New York: McGraw-Hill.
  7. Schoenwolf, G. C., et al. (2015). Second week: Becoming bilaminar and fully implanting. In: Schoenwolf, G. C., et al. (Eds.), Larsen’s Human Embryology. Philadelphia: Elsevier, Saunders, pp 43–56.
  8. Ross, M.G., Beall, M.H. (2021). Physiology of amniotic fluid volume regulation. Retrieved July, 5, 2021, from https://www.uptodate.com/contents/physiology-of-amniotic-fluid-volume-regulation

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