velamentous

Velamentous is an obstetric term used to describe conditions in which placental or umbilical cord vessels course through the membranes before reaching the placental tissue, rather than traveling within the placental parenchyma. The term derives from velamentum, meaning a veil or membrane.

The two main manifestations are velamentous cord insertion and velamentous placentation. Velamentous cord insertion occurs when the umbilical vessels insert into the fetal membranes (chorion and amnion) rather than the placental disc. The vessels then traverse the membranes for a distance before reaching the placental tissue, lacking the protective cushion of Wharton’s jelly. This arrangement increases the risk of vessel rupture or compression, particularly if the membranes rupture, and is associated with fetal growth restriction, preterm birth, and, in some cases, vasa previa, in which vessels lie across the cervical os and are vulnerable during membrane rupture.

Velamentous placentation refers to abnormal placental attachment in which placental vessels travel through the membranes before entering the placental parenchyma. This configuration can be linked with placental or obstetric complications, including fetal growth restriction and preterm delivery, and it can contribute to vasa previa when vulnerable vessels cross the birth canal or os.

Diagnosis is usually by prenatal ultrasound with color Doppler, which can identify abnormal cord insertion or exposed vessels within the membranes. Postnatal placental examination confirms the finding. Management involves careful prenatal surveillance and delivery planning; cesarean delivery may be indicated if there is vasa previa or other high-risk features to minimize fetal risk.