Circumvallate placenta is a rare condition affecting about 1–2% of pregnancies, in which the amnion and chorion fetal membranes essentially "double back" on the fetal side around the edges of the placenta. After delivery, a circumvallate placenta has a thick ring of membranes on its fetal surface. Circumvallate placenta is a placental morphological abnormality associated with increased fetal morbidity and mortality due to the restricted availability of nutrients and oxygen to the developing fetus.
Physicians may be able to detect a circumvallate placenta during pregnancy by using an ultrasound. However, in other cases, a circumvallate placenta is not identified until delivery of the baby. Circumvallate placenta can increase the risk of associated complications such as preterm delivery and placental abruption. Occasionally, a circumvallate placenta can also increase the risk of neonatal death and emergency caesarean section. Although there is no existing treatment for circumvallate placenta, physicians can attempt to minimize the effects of complications, if they occur, through frequent fetal monitoring and, if necessary, emergency cesarean section.
In a circumvallate placenta, the chorionic plate, which forms the fetal surface of the placenta, tends to be smaller than the basal plate, which forms the maternal surface of the placenta. This results in the elevation of the placental margin and the appearance of an annular shape. The fetal surface is divided into a central depressed zone surrounded by a thickened white ring which is incomplete. The ring is situated at varying distances from the margin, or edges, of the placenta. This thick ring of membranes is composed of a double fold of amnion and chorion with degenerated decidua vera and fibrin in between. Blood vessels, supplying nutrients and carrying waste products to and from the developing fetus, radiate from the umbilical cord insertion to as far as the ring of membranes, and then disappears from view.
Signs and symptoms A circumvallate placenta does not always induce associated symptoms during pregnancy, making it extremely difficult to diagnose a circumvallate placenta in asymptomatic mothers. In symptomatic mothers, physicians may be able to detect a circumvallate placenta based on the presentation of the following signs.
Vaginal bleeding: A circumvallate placenta can increase the risk of frequent vaginal bleeding during the first trimester of pregnancy. In a study conducted with 92 women with a circumvallate placenta, it was concluded that incidences of vaginal bleeding were significantly higher in women with a circumvallate placenta during all three trimesters when compared to the control group. However, a noted limitation of the study considered by the researchers was that because the study included such a small number of women, the obtained results may not be fully representative of the general population. Because the chorionic plate is much smaller than the basal plate in a circumvallate placenta, vaginal bleeding tends to occur at this site where the placenta is exposed and uncovered. In mothers presenting with vaginal bleeding, circumvallate placenta should be suspected as a possible cause of the vaginal bleeding. Inhibited fetal growth: Fetuses tend to develop more slowly when associated with a circumvallate placenta, largely due to the reduced supply of blood and nutrients from mother to fetus. Physicians will order tests to determine the cause of inhibited fetal growth when a developing fetus does not meet growth expectations during the course of the pregnancy. Premature rupture of membranes (PROM): PROM happens when the protective covering of the amniotic sac ruptures before the onset of labor and delivery. If PROM occurs within the first 37 weeks of pregnancy, it is termed preterm premature rupture of membranes (PPROM). PROM itself has many causes and risk factors. When PROM occurs along with vaginal bleeding in the second trimester of pregnancy, it is suspected that a mother likely has a circumvallate placenta.
Complications Circumvallate placenta has also been associated with a higher incidence of complications including placental abruption, low birth weight, premature delivery, perinatal death, and fetal abnormalities.
Low birth weight: Lack of proper nutrition and blood flow to the fetus during pregnancy often results in decreased weight of the baby at birth. Placenta abruption: Placenta abruption, in which the placenta divides from the wall of the uterus prior to birth, can have severe outcomes for a mother and her baby. Such consequences include vaginal bleeding, decreased birth weight, preterm delivery, and stillbirth. Significant vaginal bleeding can induce maternal anemia and dangerously low blood pressure. Oligohydramnios: Insufficiency of proper volumes of amniotic fluid, a condition called oligohydramnios, can also occur as a result of a circumvallate placenta. Amniotic fluid is essential to normal fetal movement, fetal organ development, and cushioning of the fetus within the mother's uterus. It is also imperative in preventing umbilical cord compression so that the fetus is able to obtain nourishment and oxygenation from its mother. Premature delivery: Premature birth of the fetus occurs at less than 37 weeks of gestation, compared to full-term delivery at about 40 weeks. Miscarriage: Loss of a fetus prior to birth via miscarriage can transpire if any of the above complications occur without prompt intervention and treatment.
Cause Unfortunately, there is no known cause of circumvallate placenta and no major preventative measures that can be taken to minimize the risk of developing a circumvallate placenta. Circumvallate placenta is not a genetic disorder. Some potential causes of circumvallate placenta include reduced amniotic fluid pressure, circumferential hemorrhage, and superficial or deep implantation of the embryo within the uterine wall, although these potential causes are still not well-understood in terms of their relation to circumvallate placenta.
High-risk pregnancies are described as pregnancies in which a mother, the fetus, or both are put at a higher risk for developing pregnancy complications before, during, or after birth. Risk factors such as hypertensive medical conditions, maternal age, and substance use are just some of the things that can put a woman at an increased risk for developing circumvallate placenta and/or any other complications.
Risk factors
Hypertensive disorders Women entering a pregnancy with hypertension are considered to be put at a higher risk for preeclampsia or eclampsia during the course of their pregnancy. Hypertensive disorders, like hypertension, have been found to affect about 10% of pregnancies in the United States and have resulted in about 6.8% of maternal deaths from 2011 to 2015. High blood pressure during pregnancy can potentially damage maternal organ systems such as the liver or the kidneys, which can be life-threatening. To prevent preeclampsia or eclampsia from developing in pregnancy, women with hypertension can be prescribed anti-hypertensive medications during pregnancy and are advised to monitor their blood pressure throughout the course of pregnancy.
Maternal age Another risk factor for developing any pregnancy complications is maternal age. Advanced maternal age, considered to be when a woman enters pregnancy at age 35 or above, has also been linked to increased risk of maternal mortality, preeclampsia, restricted fetal growth, fetal distress, and a variety of other pregnancy complications. Conversely, teenage pregnancy is also associated with increased risk of endometriosis, postpartum hemorrhage, and mild preeclampsia, when compared with pregnant mothers in their 20s. Genetically, the long period of time between meiotic arrest of the egg gamete as a fetus and each ovulation cycle occurring after the onset of female puberty in teenage years can potentially contribute to the increased risk for pregnancy complications in mothers who are age 35 or older at time of pregnancy.
Substance use Further, yet another factor inducing adverse complications in pregnancy is substance use status. Nicotine, alcohol, and marijuana are the most common substances used during pregnancies. Substance use in pregnancy is concerning because of its alarming association with other risk factors, such as mental illness. Depression alone has been associated within increased risk for preeclampsia, gestational diabetes, hypertension, premature birth, and low birth weight. Women with substance use disorders tend to live in areas that are unable to provide quality prenatal care or proper management of their psychiatric conditions. As a result of improper management of psychiatric illnesses, substances are abused during pregnancy, potentially causing harm to both the mother and the fetus. Some pregnancy complications that can occur as a result of substance use in pregnancy are fetal alcohol syndrome and neonatal abstinence disorder.
Women with these risk factors are recommended additional surveillance during pregnancy to monitor fetal development and to be able to detect fetal, placental, or umbilical cord abnormalities as early as possible.
Pathophysiology or mechanism The placenta is a transient organ developed during pregnancy that facilitates nutrient, gas, and waste exchange between a mother and a developing fetus. Placental abnormalities, such as circumvallate placenta, can harm a developing fetus, as normal exchange of materials between a mother and a developing fetus is impaired. With placental abnormalities, a developing fetus is unable to receive the vital materials that it needs for proper development, resulting in the possibility of pregnancy complications, birth defects, and/or death of the fetus.
In a normal placenta, there is a smooth transition from the parenchymal villous chorion to the membranous chorion at the border of the placental plate. Fetal blood vessels subdivide from the umbilical cord and spread diagonally throughout the parenchyma towards the edge of the placental plate.
In a circumvallate placenta, the membranes often become restrained due to marginal infarct, hemorrhage, or fibrin depositing. This results in the reduction in size of the chorionic plate of the placenta, further causing the membranes on the fetal side to fold backward on themselves. The parenchymal villous chorion continues to proliferate beyond the tethered membranes and appears to protrude outward. The fetal blood vessels are directed downward and then horizontally in order to provide blood flow to the most peripheral parts of the placental plate extending beyond the tethered membranes.
Since a portion of the placenta tends to become exposed in a circumvallate placenta, due to the reduced size of the chorionic plate, vaginal bleeding is more likely to occur at this site of exposure. Likewise, inhibited fetal growth can also ensue due to the decreased exchange of nutrients and waste between mother and fetus, since the fetus is unable to sustain necessary nutritional demands for proper fetal development. Premature rupture of membranes often occurs as a result of infection in the uterus, which can be caused by the occurrence vaginal bleeding. Therefore, placental abnormalities such as circumvallate placenta can be extremely detrimental in causing the onset of associated conditions.
Diagnosis In some cases, a physician may be able to diagnose a circumvallate placenta via ultrasound during one of many routine ultrasound screenings. In most cases, a circumvallate placenta is not discovered until physical examination of the placenta after delivery of the fetus. For this reason, circumvallate placenta is very difficult to diagnose during pregnancy.