The following is associated with increased risk for :-

Velamentous placenta - The umbilical cord vessels travel within the membrane before reaching placental margin . - Rupture of the membranes involving the overlying vessels lead to vaginal bleeding. - As it is entirely fetal blood, this may result in fetal exsanguination and even death in more than 50% of cases. This condition is actually called 'Vasa pre" when these membraneous vessels overlie the cervical os