Velamentous Cord Insertion

In velamentous cord insertion the umbilical cord inserts into the fetal membranes (chorioamniotic membranes) rather than into the placental disc, so the umbilical vessels run unprotected by Wharton jelly through the membranes to reach the placental edge.

Incidence is about 1% of singleton pregnancies, 8 to 15% of monochorionic twin pregnancies, and higher in IVF pregnancies, placenta praevia, low lying placenta, advanced maternal age, smoking, primiparity, and maternal diabetes. It is related to the "trophotropism" theory (the placenta atrophies on the side of lower decidual perfusion).

Complications: vasa previa (if the vessels cross the internal os), cord compression or rupture, fetal growth restriction, preterm birth, low Apgar scores, perinatal mortality and retained placenta.

• Usually asymptomatic and diagnosed on ultrasound or at delivery
• Fetal heart rate abnormalities (variable decelerations) and fetal growth restriction
• Vaginal bleeding with membrane rupture (if vasa previa)
• At delivery: cord avulsion during traction (risk of haemorrhage), and the cord appears to attach to membranes at a distance from the placental margin
• Association with single umbilical artery, congenital anomalies, and twin pregnancies

• Second trimester ultrasound: cord insertion location (an eccentric or marginal insertion should be reported), with colour Doppler to show vessels traversing membranes
• Transvaginal ultrasound if the placenta is low lying, to exclude vasa previa
• Third trimester growth ultrasound and Doppler of umbilical artery
• Pathological examination of the placenta after delivery confirms the diagnosis

• Antenatal: confirm no vasa previa; follow up growth scans every 3 to 4 weeks from 28 weeks for increased risk of fetal growth restriction; fetal surveillance with umbilical artery Doppler and non-stress tests if growth restricted.
• If vasa previa is present: manage as vasa previa (planned caesarean at 34 to 36 weeks).
• Labour: avoid cord traction at delivery of the placenta (controlled cord traction should be cautious to reduce avulsion), with active management of the third stage, and recognition of the risk of retained placenta; monitor the fetus continuously in labour.
• Delivery mode is decided by obstetric indications; caesarean not routinely required in the absence of vasa previa.
• Send the placenta for histology in cases with growth restriction or adverse outcome.
• Counsel regarding recurrence (low).