Vasa praevia

Vasa praevia or vasa previa is a complication of obstetrics in which fetal blood vessels cross or run near the internal opening of the uterus. Since these vessels are not protected by the umbilical cord or placental tissue, the rupture of the fetal membranes during birth causes them also to rupture, leading rapidly to death of the fetus. The term is derived from the Latin; vasa means "vessels" and praevia comes from pre meaning "before" and via meaning "way". In other words, vessels lie before the fetus in the birth canal and in the way.

Risk factors include low-lying placenta and in vitro fertilization. Vasa praevia occurs in about 0.6 per 1,000 pregnancies.