Velamentous (membranous) insertion: Occurs in 1% of singletons and in almost 15% of twins. The cord inserts into the membranes far away from the placental margin. Umbilical vessels run unprotected by Whartons jelly and are vulnerable to injury. Velamentous vessels run over the internal os are called vasa previa. These vessels are at risk of rupture during delivery. The mortality of vasa previa hemorrhage is very high, the fetus exsanguinates within minutes. Velamentous insertion can be detected before the delivery using color Doppler ultrasound. The fetus is delivered by elective cesarean section.

Marginal insertion: Insertion at the placental margin (battledore placenta) occurs in 5 – 7% pregnancies.