The placenta is a temporary organ that forms in the uterus during pregnancy, serving as a vital connection between the pregnant individual and the developing fetus. It facilitates the exchange of oxygen and nutrients, removes waste products, and produces essential hormones that support pregnancy. While typically disc-shaped with smooth edges, the placenta can sometimes develop with an abnormal configuration, such as a circumvallate placenta. This rare condition affects approximately 1% to 2% of pregnancies, involving a unique folding of the fetal membranes.
What Circumvallate Placenta Is
A circumvallate placenta is a distinctive structural abnormality where the fetal membranes double back on the fetal side around the edges of the placenta. This creates a thickened, raised ring of membranes on the fetal surface, giving the placenta a “pizza-like” appearance with raised edges rather than a flat disc. In a normal placenta, there is a seamless transition where fetal blood vessels spread uniformly to the edges, but with a circumvallate placenta, these vessels terminate abruptly at the inner margin of the fibrous ring, rather than extending to the true placental edge.
This condition arises because the chorionic plate, the fetal surface, is smaller than the basal plate, the maternal surface attached to the uterine wall. This size discrepancy causes the fetal membranes to fold inward and fuse some distance from the actual placental margin. The exact cause is not fully understood, but theories include abnormal embryo implantation, either too superficially or too deeply within the uterine wall.
Another proposed mechanism involves early marginal hemorrhage or fibrin deposition, which can restrain the membranes and reduce the chorionic plate’s size. This causes the membranes to fold backward, forming the characteristic ring. Reduced amniotic fluid pressure has also been considered a potential contributing factor.
Effects and Care
A circumvallate placenta can lead to various implications for both the pregnant individual and the developing fetus. Common signs include persistent vaginal bleeding, which can occur throughout the first and second trimesters. This bleeding may be linked to the exposed portion of the placenta within the circumvallate ring. The condition also increases the likelihood of premature rupture of membranes (PROM), where the amniotic sac breaks before labor begins, potentially leading to preterm birth if it occurs before 37 weeks of gestation.
Fetal growth restriction, often resulting in a low birth weight, is another significant concern associated with circumvallate placenta. This can happen due to reduced blood flow and nutrient exchange across the compromised placental surface. There is also an increased risk of placental abruption, a serious condition where the placenta separates from the uterine wall prematurely, causing severe bleeding and compromising fetal oxygenation. Insufficient amniotic fluid, known as oligohydramnios, can also occur, impacting fetal movement, development, and umbilical cord cushioning.
Diagnosing a circumvallate placenta during pregnancy can be challenging, often identified only after delivery upon examination of the placenta. However, prenatal diagnosis is possible through ultrasound, which may reveal irregular edges, uplifted margins, or a distinctive echodense ridge, sometimes called a “placental shelf.” If diagnosed, there is no specific treatment to reverse the condition itself. Instead, medical care focuses on close monitoring and managing potential complications to optimize outcomes for both parent and baby.
Management typically involves frequent fetal monitoring, including regular growth assessments, sometimes monthly or weekly if blood flow concerns are present. In cases of oligohydramnios, amnioinfusion, which introduces fluid into the amniotic sac, may be considered. If complications become severe or the fetus shows signs of distress, early delivery may be necessary, and corticosteroids might be administered to accelerate fetal lung development.