Vasa praevia is a condition in which fetal blood vessels cross or run near the internal opening of the uterus.

These vessels may be from either a velamentous insertion of the umbilical cord or may be joining an accessory (succenturiate) placental lobe to the main disk of the placenta.

Vasa previa is seen more commonly with velamentous insertion of the umbilical cord, accessory placental lobes (succenturiate or bilobate placenta [fr]), multiple gestation, and in vitro fertilisation pregnancy.

The reasons for this association are not clear, but disturbed orientation of the blastocyst at implantation, vanishing embryos and the increased frequency of placental morphological variations in IVF pregnancies have all been postulated[citation needed].

Given the timing of membrane rupture is difficult to predict, elective cesarean delivery at 35–36 weeks is recommended.

Because these patients are at risk for preterm delivery, it is recommended that steroids should be given to promote fetal lung maturation.