An uncommon but potentially disastrous complication of delivery, occurring in about 1 in 5000 deliveries, when unprotected fetal vessels run across the lower uterine segment and cervix in front of the presenting part of the fetus. It is associated with a velamentous insertion of the cord (where the umbilical cord inserts directly into the membranes rather than the placenta) and in cases with normal cord insertion when the vessels run between the two lobes of a bilobed placenta. Vessels unsupported by placental tissue or the umbilical cord can tear when the cervix dilates or the membranes rupture, causing rapid fetal haemorrhage. Immediate Caesarean section to save the baby from exsanguination is indicated. Fetal mortality for cases not recognized before the onset of labour is very high; appropriate use of prenatal ultrasonography may prevent perinatal death.
Subjects: Medicine and Health.