What is a Circumvallate Placenta?
A circumvallate placenta is a morphological abnormality of the fetal membranes where the chorionic plate is smaller than the basal plate, causing the fetal membranes to fold back upon themselves at the placental margin, creating a characteristic raised ring or shelf on the fetal surface of the placenta. 1
Pathophysiology and Distinction from Other Placental Abnormalities
Circumvallate placenta is fundamentally different from placenta accreta spectrum disorders - it involves abnormal membrane insertion rather than abnormal trophoblast invasion into the myometrium 1
The condition occurs when there is peripheral detachment of the membranes from the chorionic plate, with subsequent infolding creating a raised edge or shelf 2, 3
This is a structural variant of placenta extrachorialis, where the transition from membranous to villous chorion occurs inward from the placental edge 2
Sonographic Features
The key ultrasound finding is an infolding of the fetal membrane upon the fetal surface of the placenta, typically identified during the second trimester 2
By the third trimester, the appearance may change to show only a bright border or shelf at the periphery of the placenta 2
Additional sonographic features include an irregular placental edge, uplifted margin, or visible placental sheet/shelf at the margin 3, 4
Clinical Significance and Pregnancy Outcomes
The clinical significance of prenatally diagnosed circumvallate placenta remains controversial, with recent evidence suggesting better outcomes than historically reported:
A 2024 study found that prenatal ultrasound diagnosis of circumvallate placenta was NOT associated with adverse pregnancy outcomes when compared to matched controls, suggesting that prenatal diagnosis may not warrant additional surveillance 5
However, older retrospective data (2014) reported associations with preterm delivery (64.1%), placental abruption (10.9%), emergency cesarean section (45.6%), small-for-gestational age infants (36.9%), and neonatal complications 6
The condition has been associated with second-trimester vaginal bleeding and premature chemical rupture of membranes (PCROM) 6
Diagnostic Accuracy
Prenatal sonographic diagnosis of circumvallate placenta has poor accuracy:
A 1997 study demonstrated that experienced sonologists achieved ROC curve values of only 0.39 to 0.58 for detecting circumvallation, indicating poor diagnostic performance 4
In that study, 35% of normal placentas were misclassified as circumvallate, and most true cases of circumvallation were missed or graded as normal 4
The diagnosis is typically made at a mean gestational age of 19.8 weeks when identified prenatally 5
Clinical Management Implications
Given the most recent evidence showing no association with adverse outcomes when prenatally diagnosed, additional surveillance may not be necessary 5
The diagnosis is definitively confirmed only after delivery by gross and microscopic pathologic examination 3, 4
When vaginal bleeding and PCROM occur together during pregnancy, circumvallate placenta should be considered in the differential diagnosis, though the sensitivity of these clinical features is only 28.8% 6