The placenta is the temporary organ that develops during pregnancy, acting as the interface between the mother and the fetus to facilitate the exchange of nutrients, oxygen, and waste. Circumvallate placenta (CP) is a structural variation where the fetal membranes fold back on themselves, creating an abnormality in the placenta’s shape. This condition is relatively uncommon, occurring in about 1-2% of pregnancies, and many affected pregnancies progress without significant issues. However, the diagnosis signals a need for focused attention and monitoring, as this structural change can potentially affect the pregnancy’s course.
The Anatomy of Circumvallate Placenta
A normal placenta has a smooth, flat fetal surface (the chorionic plate) extending uniformly to the edge. In a circumvallate placenta, the chorionic plate is smaller than the basal plate (the surface attached to the uterine wall). This size mismatch causes the fetal membranes (the amnion and chorion) to double back and roll inward from the placental edge.
This folding creates a raised, thickened ring or ridge on the fetal surface, set inward from the actual placental margin. This ring is composed of a double layer of amnion and chorion. The result is an appearance often described as a “pizza with raised edges,” where the membranes attach centrally rather than at the periphery. This altered attachment effectively reduces the functional area of the placenta, which is the mechanism believed to lead to potential complications.
Identifying a Circumvallate Placenta
Diagnosing a circumvallate placenta is challenging during pregnancy and is frequently only confirmed after delivery when the placenta is visually inspected. However, prenatal detection is possible, typically occurring during a routine second-trimester ultrasound, usually around 20 weeks of gestation.
The sonographer looks for specific features indicating the abnormality, such as an irregular placental edge or an uplifted margin. A characteristic finding is the “placental shelf,” a ridge of tissue that protrudes into the amniotic cavity. The ability to accurately detect the condition with ultrasound varies, and sometimes a normal placenta may be incorrectly identified as circumvallate. If detected early, the finding may disappear by the time of the mid-pregnancy scan.
Potential Complications During Pregnancy
The structural changes of a circumvallate placenta can affect the efficiency of placental exchange and increase the risk for adverse outcomes, though many pregnancies remain uncomplicated. The restricted blood flow or nutrient exchange in the rolled margin is the proposed reason for potential complications.
Fetal Risks
One common fetal risk is Fetal Growth Restriction (FGR), resulting in a baby who is small for gestational age or has a low birth weight. The abnormal placental surface is also associated with oligohydramnios, a reduced amount of amniotic fluid. This reduction in fluid volume can increase the risk of umbilical cord compression. The condition is also linked to a higher incidence of preterm delivery.
Maternal and Delivery Risks
A separate concern is placental abruption, where the placenta prematurely separates from the inner wall of the uterus, causing significant bleeding. Maternal risks, while less frequent, include a higher chance of antepartum or postpartum bleeding. Occasionally, a cesarean section may be necessary due to complications. Some studies also report a higher risk of neonatal death and admission to the Neonatal Intensive Care Unit (NICU).
Monitoring and Management Strategies
When a circumvallate placenta is diagnosed prenatally, the standard approach involves heightened surveillance, though some evidence suggests an isolated finding may not require additional monitoring. The primary goal of management is to monitor for potential complications.
Management typically includes more frequent prenatal appointments and specialized ultrasounds to track the baby’s development. Serial growth scans are performed to assess fetal growth and identify signs of Fetal Growth Restriction early. The volume of amniotic fluid is also monitored closely to detect oligohydramnios.
Any vaginal bleeding, particularly in the second trimester, should be promptly evaluated, as this is a known symptom. The diagnosis does not automatically necessitate a cesarean section, and a vaginal delivery is often possible. The timing and method of delivery are ultimately determined by the overall health of the mother and baby and the presence of complications, such as restricted growth or fetal distress.