Placental Abnormalities

Normal placental structure and function are essential for a healthy pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care. Some of the most common placental abnormalities include structural anomalies (such as a succenturiate lobe or velamentous cord insertion), implantation anomalies (such as placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity accreta and placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity previa), and functional anomalies (such as placental insufficiency). The placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity is typically seen well on ultrasound, and placental assessment is part of routine antenatal screening, which is when most structural and implantation anomalies are identified. Because of the extensive maternal and fetal circulation through the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity, placental abnormalities can significantly increase the risk of serious antepartum or postpartum hemorrhage Postpartum hemorrhage Postpartum hemorrhage is one of the most common and deadly obstetric complications. Since 2017, postpartum hemorrhage has been defined as blood loss greater than 1,000 mL for both cesarean and vaginal deliveries, or excessive blood loss with signs of hemodynamic instability. Postpartum Hemorrhage. Placental abnormalities also frequently impact decisions regarding the timing and route of delivery.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

The placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity is an important structure for fetal growth and development during embryonic and fetal life. Abnormalities in its structure, function, or implantation can result in serious and potentially fatal complications for both the fetus and mother.

Placental structure and circulation

  • Chorionic villi provide a large surface area for maternal-fetal exchange.
  • Spiral 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 (maternal) fill the intervillous spaces in the decidua basalis layer of the endometrium:
    • Bring in oxygenated blood for the fetus
    • The spiral 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 “rupture” and become large spaces called lacunae, which:
      • Are extremely low-resistance areas
      • Do not have the ability to regulate blood flow through the organ
  • 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 bring deoxygenated blood from the fetus to the placental chorionic villi.
  • Exchange of gases and molecules occurs between the fetal blood in the chorionic villi and maternal blood in the lacunae, across the placental barrier.
  • Umbilical vein 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 carry deoxygenated blood back to the maternal circulation.
  • Maternal and fetal blood never come into direct contact.
  • Fetal hemoglobin has ↑ affinity for O2 compared with maternal hemoglobin → causes O2 to move from maternal RBCs to fetal RBCs

Functions of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity

  • 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 and CO2)
  • Nutrient exchange
  • Fetal waste removal
  • Hormone production (a fetal and maternal endocrine organ during pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care):
    • HCG
    • Human placental lactogen (hPL)
    • Chorionic thyrotropin
    • Chorionic corticotropin-releasing hormone (CRH)
    • Progesterone
    • 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 to support the fetus:
    • Glycogen and cholesterol synthesis
    • Protein metabolism
  • Assists in rejection of the maternal immune system

Normal placental implantation

  • Early fetal trophoblastic cells invade into the maternal decidua basalis layer of the endometrium:
    • Trophoblastic cells should not invade into the myometrium beneath the endometrium.
    • When trophoblastic cells do invade into the myometrium, the condition is called placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity accreta.
  • Placentas typically implant in the fundal region of the uterus:
    • The placental edge should be away from the internal cervical os.
    • When the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity covers the internal cervical os, the condition is called placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity previa. 
    • When the placental edge is within 2 cm of the cervical os, it is called low-lying placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity.
  • The placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity should remain connected to the maternal endometrium, providing O2 and nutrients, until after the delivery of the infant.
    • When the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity separates early, the condition is called placental abruption. 
    • When the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity fails to provide adequate O2 or nutrients to the fetus, the condition is called placental insufficiency.

Structural Abnormalities of the Placenta and Umbilical Cord

Bilobate and succenturiate placentas

  • Bilobate placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity: 
    • Separation of the placental forms into nearly equal-sized lobes with the umbilical cord inserted between them
    • Incidence: 1 in 350 deliveries
  • Multilobate placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity: Placenta has ≥ 3 lobes.
  • Succenturiate lobe:
    • 1 or more smaller lobes develop.
    • Lobes often develop at a distance from the main placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity, but with a vascular connection.
    • More common with twins
  • Diagnosis: Placentas are easily seen on ultrasound, and abnormal structures are typically identified on routine antenatal ultrasound.
  • Complications:
    • ↑ Risk of postpartum hemorrhage Postpartum hemorrhage Postpartum hemorrhage is one of the most common and deadly obstetric complications. Since 2017, postpartum hemorrhage has been defined as blood loss greater than 1,000 mL for both cesarean and vaginal deliveries, or excessive blood loss with signs of hemodynamic instability. Postpartum Hemorrhage due to retained placental tissue (e.g., the main lobe delivered but the succenturiate lobe did not)
    • Vessels connecting the main placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity with the succenturiate placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity may rupture 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 causing fetal hemorrhage/demise.
    • ↑ Risk of vasa previa (see below)

Velamentous cord insertion

  • Definition: 
    • The last few centimeters of the umbilical cord entering the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity lack the protective Wharton’s jelly.
    • The vessels are “exposed” and covered only by the fetal membranes.
  • Epidemiology: 1% of all pregnancies
  • Risk factors:
    • Multiple pregnancies, mainly twin gestations
    • Placenta previa
  • Diagnosis: Antenatal ultrasound shows a cord that does not insert centrally into the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity.
  • Management:
    • Intrapartum: Continuous fetal heart rate monitoring and C-section delivery should be considered.
    • Antepartum: If velamentous insertion overlies the cervix, an elective C-section should be scheduled for 35 weeks gestation.
  • Complications:
    • Vessels are much more vulnerable to rupture.
    • Vascular compression → fetal morbidity and mortality
    • Much higher risk of vasa previa and antenatal hemorrhage
Velamentous cord insertion placental abnormalities

Velamentous cord insertion:
Note that for the last several centimeters, there is no protective Wharton’s jelly surrounding the vessels; they are covered only by a thin fetal membrane.

Image: “Velamentous cord insertion” by Schokohäubchen. License: Public Domain

Vasa previa

  • Definition: occurs when fetal blood vessels traverse or run near the internal cervical os 
  • Epidemiology: 1 in 5200 pregnancies
  • Associated risk factors:
    • Velamentous umbilical cord 
    • Succenturiate placental lobes
    • Pregnancies conceived via in vitro 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 (IVF)
    • Multiple gestations
  • Clinical presentation: triad consisting of:
    • Membrane rupture
    • Painless vaginal bleeding (fetal blood)
    • Fetal bradycardia (HR < 110/min)
  • Diagnosis:
    • Confirmed by examination of placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity after delivery
    • Suspected in antenatal sonogram with color flow doppler 
  • Management: 
    • Pelvic rest (no digital exams, no intercourse; “nothing in the vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor”) antenatally
    • Immediate 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 for clinical bleeding and/or signs 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
  • Complications: blood vessels rupture → bleeding from fetoplacental circulation → fetal exsanguination and death
Ultrasound image of a vasa previa placental abnormalities

Ultrasound image of vasa previa:
The doppler color flow is illuminating the fixed vessels traversing the internal cervical os. The cervical canal is shown with a yellow dotted line.

Image: “Measurement of the cervical length by color Doppler transvaginal examination” by Bohîlțea RE et al. License: CC BY 2.0

Other anomalies of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity and umbilical cord

  • Single umbilical artery (may ↑ the risk of aneuploidy or other associated anomalies)
  • Marginal cord insertion: 
    • Insertion of the cord near the edge of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity rather than in the middle
    • May ↑ the risk of the cord being torn off during delivery of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity 
  • Umbilical cord loops and/or knots, which may impede blood flow.
  • Funic presentation:
    • When a loop of the normal umbilical cord is tucked below the fetal presenting part
    • ↑ Risk for cord prolapse or fetal distress due to cord compression
    • Typically requires C-section

Placenta Accreta Spectrum

Definition

Placenta accreta spectrum (PAS) describes a spectrum of abnormal placentation in which the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity is abnormally and firmly adherent to the uterine wall. The 3 degrees of PAS are:

  • Placenta accreta (approximately 65%): The placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity attaches directly to the myometrium due to partial or total absence of the decidua basalis.
  • Placenta increta (15%): Placental villi invade into the myometrium.
  • Placenta 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

Epidemiology and pathogenesis

  • The prevalence has been increasing steadily over the past few decades and is now approximately 0.2% of pregnancies.
  • Likely due to defective decidualization in an area of scar caused by prior uterine surgery

Risk factors

  • Placenta previa after a prior C-section:
    • Most important risk factor
    • > 60% chance of PAS after 4 C-sections if placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity previa is present
  • Prior history of uterine surgery/procedures: 
    • Cesarean delivery
    • Myomectomy
    • Dilation and curettage
    • Endometrial ablation
  • Infertility Infertility Infertility is the inability to conceive in the context of regular intercourse. The most common causes of infertility in women are related to ovulatory dysfunction or tubal obstruction, whereas, in men, abnormal sperm is a common cause. Infertility procedures
  • Maternal age > 35 years
  • Multiparity
  • Postpartum endometritis Endometritis Endometritis is an inflammation of the endometrium, the inner layer of the uterus. The most common subtype is postpartum endometritis, resulting from the ascension of normal vaginal flora to the previously aseptic uterus. Endometritis
  • If the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity requires manual removal

Diagnosis

  • Typically asymptomatic
  • Usually diagnosed on routine antenatal ultrasound
  • If missed on ultrasound, PAS is typically diagnosed at delivery when the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity fails to deliver. 
    • Massive postpartum hemorrhage Postpartum hemorrhage Postpartum hemorrhage is one of the most common and deadly obstetric complications. Since 2017, postpartum hemorrhage has been defined as blood loss greater than 1,000 mL for both cesarean and vaginal deliveries, or excessive blood loss with signs of hemodynamic instability. Postpartum Hemorrhage can result when manual separation of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity is attempted.
    • Therefore, when attempting manual removal of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity:
      • Try to find the natural tissue plane between the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity and the uterus, and pull it out intact.
      • Do not create a plane by ripping the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity.

Management

  • Planned 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
  • For placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity increta and percreta, concurrent hysterectomy is often required → patients require extensive counseling

Complications

  • Severe postpartum hemorrhage Postpartum hemorrhage Postpartum hemorrhage is one of the most common and deadly obstetric complications. Since 2017, postpartum hemorrhage has been defined as blood loss greater than 1,000 mL for both cesarean and vaginal deliveries, or excessive blood loss with signs of hemodynamic instability. Postpartum Hemorrhage secondary to retained placental tissue (blood is entering maternal lacunae that are now “open” without the fetal chorionic plate being present)
  • Complications related to hypovolemic/hemorrhagic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock, including postpartum hypopituitarism Hypopituitarism Hypopituitarism is a condition characterized by pituitary hormone deficiency. This condition primarily results from a disease of the pituitary gland, but it may arise from hypothalamic dysfunction. Pituitary tumors are one of the most common causes. The majority of cases affect the anterior pituitary lobe (adenohypophysis), which accounts for 80% of the gland. Hypopituitarism (i.e., Sheehan syndrome)

Placenta Previa

Definition

Placenta previa refers to the presence of placental tissue covering the internal cervical os. When the cervix begins dilating, the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity will become “detached” over the opening cervical os, resulting in life-threatening fetal hemorrhage.

Location of the placenta in placenta previa

Location of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity in placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity previa

Image: “Placenta previa” by OpenStax College – Anatomy & Physiology. License: CC BY 3.0

Risk factors

  • Previous placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity previa
  • Previous 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 uterine procedures (e.g., dilation and curettage)
  • Multiple gestations
  • Multiparity
  • Maternal cocaine use

Diagnosis

  • Typically diagnosed on routine antenatal ultrasound, which shows the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity over the cervical os
  • If missed on ultrasound, may present with painless bright-red bleeding: 
    • Often occurs after a digital exam or intercourse
    • Can be differentiated from placental abruption, which presents with painful bleeding and uterine irritability

Management

  • Note: Approximately 90% of previas identified at < 20 weeks gestation will resolve as the lower uterine segment grows, “moving” the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity further away from the cervical os.
    • Resolution is more likely when only the edge of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity is touching the edge of the cervix.
    • Less likely to resolve when the os is completely covered
  • Pelvic rest 
  • Avoid digital exams (cervical dilation should be assessed visually with a speculum exam).
  • Follow with serial ultrasounds to look for resolution.
  • Planned 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 if placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity previa remains at full term (or at 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)

Complications

  • Preterm delivery (approximately 45% of patients)
  • Antenatal hemorrhage (approximately 50% of patients)
  • Postpartum hemorrhage (approximately 25% of patients)
  • Risk of recurrence in subsequent pregnancies (4%‒8% of patients)

Uteroplacental Insufficiency

Definition

Uteroplacental insufficiency may be acute or chronic and refers to the inability of the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity to deliver a sufficient supply of O2 and nutrients to the fetus.

Chronic uteroplacental insufficiency

Chronic uteroplacental insufficiency results in 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 associated complications.

  • Etiology/risk factors:
    • Maternal vascular disease, especially:
      • Chronic hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
      • Preeclampsia
      • Pregestational diabetes
    • Severe maternal 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
    • Maternal smoking or cocaine use
    • Uterine malformations
  • Diagnosis via ultrasound, demonstrating:
    • Fetal growth restriction
    • 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 (frequent)
    • Increased vascular resistance within the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity on Doppler studies
  • Management:
    • Patients should be monitored antenatally with frequent nonstress tests and ultrasound to look for signs of fetal decompensation.
    • Delivery is indicated when the fetus begins showing signs of distress (e.g., non-reassuring fetal status on testing).
    • Typically, if patients are otherwise candidates for vaginal delivery, induction 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 is recommended over planned 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, with close intrapartum monitoring.
    • If preterm, give a course of steroids (typically IM betamethasone) to help promote fetal lung maturity prior to delivery.

Acute uteroplacental insufficiency

  • Etiology:
    • Periods of ischemia 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 contractions, preventing the delivery of O2 and nutrients at levels required to satisfy fetal requirements 
    • Note: Relative ischemia occurs during normal 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, but can be magnified with placental pathology.
    • Partial or complete placental abruption
  • Diagnosis is via abnormalities noted on fetal cardiac monitoring:
    • Recurrent late decelerations
    • Persistent fetal bradycardia
    • Uterus is frequently hypertonic and/or tachysystolic.
  • Intrauterine resuscitation techniques: 
    • Reposition the mother (may relieve vessel compression).
    • Give mother IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids and O2 therapy to support her circulating O2 capacity.
    • ↓ Uterotonics (e.g., pitocin) and/or administer uterine tocolytics (e.g., terbutaline)
  • Expedited delivery is indicated if infants fail to respond to resuscitation, via:
    • Cesarean delivery (if remote from delivery)
    • Operative vaginal delivery (e.g., forceps or vacuum extraction) if candidates are in the 2nd 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

Clinical Relevance

The most common clinical complications of abnormal placentation are antepartum and postpartum hemorrhage Postpartum hemorrhage Postpartum hemorrhage is one of the most common and deadly obstetric complications. Since 2017, postpartum hemorrhage has been defined as blood loss greater than 1,000 mL for both cesarean and vaginal deliveries, or excessive blood loss with signs of hemodynamic instability. Postpartum Hemorrhage, which can be both severe and life threatening, depending on the clinical situation. Additionally, the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity may become infected or develop a malignancy.

  • Antepartum hemorrhage Antepartum hemorrhage Antepartum hemorrhage is defined as vaginal bleeding that occurs after 20 weeks of gestation and is unrelated to labor. The most important causes are placental abruption (most common), placenta previa (2nd most common), vasa previa, and uterine rupture. Antepartum Hemorrhage: refers to uterine bleeding that occurs 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. The most clinically important types of antepartum hemorrhage that should be immediately identified and treated include bleeding from placental abruption (typically painful), a placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity or vasa previa (typically painless), or uterine rupture (in patients with a history of major uterine surgery including a C-section delivery). Bleeding frequently affects both the mother and infant; thus, immediate delivery is indicated in most cases.
  • Postpartum hemorrhage: refers to uterine bleeding after the infant is delivered. The 4 primary causes can be remembered as the 4 T’s: Tone (uterine atony, by far the most common), Tissue (retained placental tissue), Trauma (lacerations of the perineum, vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor, or cervix), and Thrombin (coagulation disorders, especially disseminated intravascular coagulation Disseminated intravascular coagulation Disseminated intravascular coagulation (DIC) is a condition characterized by systemic bodywide activation of the coagulation cascade. This cascade results in both widespread microvascular thrombi contributing to multiple organ dysfunction and consumption of clotting factors and platelets, leading to hemorrhage. Disseminated Intravascular Coagulation). The diagnosis is typically clinical. The retained placental tissue should be removed manually or surgically.
  • Chorioamnionitis Chorioamnionitis Chorioamnionitis, commonly referred to as intraamniotic infection (IAI), is a common obstetric complication involving infection and inflammation of the fetal membranes, amniotic fluid, placenta, or the fetus itself. Chorioamnionitis is typically caused by a polymicrobial infection that ascends from the lower genitourinary tract. Chorioamnionitis (intraamniotic infection (IAI)): a common obstetric complication involving infection and inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the fetal membranes, amniotic fluid, placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity, or the fetus itself. Chorioamnionitis Chorioamnionitis Chorioamnionitis, commonly referred to as intraamniotic infection (IAI), is a common obstetric complication involving infection and inflammation of the fetal membranes, amniotic fluid, placenta, or the fetus itself. Chorioamnionitis is typically caused by a polymicrobial infection that ascends from the lower genitourinary tract. Chorioamnionitis is typically caused by an ascending polymicrobial infection from the lower genitourinary tract, most commonly after the prolonged rupture of membranes. There are specific clinical criteria for diagnosis, including maternal fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever. An IAI is managed with antibiotics, and ultimately, delivery, which typically results in its resolution.
  • 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 (GTD): a group of pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care-related tumors resulting from abnormal placental trophoblastic growth that range from benign molar pregnancies (complete and partial) to neoplastic conditions (e.g., invasive mole, choriocarcinoma, and placental site trophoblastic tumor). Patients will typically have grossly elevated serum β-hCG levels and characteristic ultrasound findings. Treatment involves surgery and/or chemotherapy, usually with methotrexate.

References

  1. Cunningham, F.G., Leveno, K.J., et al. (2010). Williams Obstetrics (23rd ed. pp. 36‒72, 557‒585).
  2. Lockwood, C.J., Russo-Stieglitz, K. (2021). Placenta previa: Epidemiology, clinical features, diagnosis, morbidity, and mortality. In Barss, V.A. (Ed.), UpToDate. Retrieved June 22, 2021, from https://www.uptodate.com/contents/placenta-previa-epidemiology-clinical-features-diagnosis-morbidity-and-mortality 
  3. Silver, R.M. (2021). Placenta accreta spectrum: Clinical features, diagnosis, and potential consequences. In Barss, V.A. (Ed.), UpToDate. Retrieved June 22, 2021, from https://www.uptodate.com/contents/placenta-accreta-spectrum-clinical-features-diagnosis-and-potential-consequences
  4. Mari, G. (2021). Fetal growth restriction: Evaluation and management. In Barss, V.A. (Ed.), UpToDate. Retrieved June 22, 2021, from https://www.uptodate.com/contents/fetal-growth-restriction-evaluation-and-management

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