What is a circumvallate placenta?

Circumvallate Placenta: Definition and Clinical Implications

A circumvallate placenta is a morphological abnormality characterized by an infolding of the fetal membranes onto the fetal surface of the placenta, creating a raised ridge or ring around the periphery of the placental disc. This condition is distinct from placenta accreta spectrum disorders, which involve abnormal placental adherence to the uterine wall.

Key Features and Diagnosis

• Circumvallate placenta presents with a characteristic raised ridge or "shelf" at the margin of the placenta, visible on ultrasound examination typically during the second trimester 1, 2
• By the third trimester, this may appear only as a bright border at the periphery of the placenta on ultrasound 1
• Definitive diagnosis is typically made after delivery by gross inspection and can be confirmed by microscopic analysis 2
• The condition occurs in approximately 0.2% of all anatomic ultrasound studies and 0.17% of all deliveries 3

Clinical Manifestations and Associated Complications

• Historically, circumvallate placenta has been associated with second-trimester vaginal bleeding when the placenta is normally implanted 1
• Additional reported complications include:
  • Preterm delivery (64.1% in affected pregnancies) 4
  • Placental abruption (10.9%) 4, 2
  • Emergency cesarean section (45.6%) 4
  • Small-for-gestational age infants (36.9%) 4
  • Neonatal death (8.9%) 4
  • NICU admission (55.4%) 4
  • Chronic lung disease (33.9%) 4

Predictive Factors and Diagnosis

• When both vaginal bleeding during the second trimester and premature chemical rupture of membranes (PCROM) occur together, circumvallate placenta should be strongly suspected (sensitivity 28.8%, specificity 99.9%) 4
• Diagnosis is typically made on ultrasound at a mean gestational age of 19.8 ± 2.4 weeks 3

Recent Evidence and Management Implications

• The most recent evidence (2024) suggests that prenatally diagnosed circumvallate placenta may not be associated with adverse pregnancy outcomes when compared to matched controls 3
• This newer finding contradicts earlier studies that reported significant adverse outcomes, suggesting that prenatal diagnosis and modern management may have improved outcomes 3
• Based on this recent evidence, additional surveillance during pregnancy may not be warranted for prenatally diagnosed circumvallate placenta 3

Pathophysiological Considerations

• Unlike placenta accreta spectrum disorders, which involve abnormal trophoblast invasion into the myometrium due to defects in the endometrial/myometrial interface 5, circumvallate placenta is a morphological abnormality of the fetal membranes
• Normal placental function involves the chorionic villi as the main functional units, where fetal blood is separated from maternal blood by the placental membrane 6
• In circumvallate placenta, the abnormal folding of membranes may affect the functional capacity of the placenta, potentially explaining some of the historically reported complications 6

Clinical Approach

• When circumvallate placenta is suspected on ultrasound, be aware of the potential for second-trimester bleeding 1, 4
• Monitor for signs of placental abruption, which has been reported as a complication in some cases 4, 2
• While older studies suggested the need for increased surveillance, the most recent evidence indicates that pregnancy outcomes may be similar to those without this condition 3