Placenta Accreta
Vasa Previa
Vasa previa refers to fetal vessels running through the membranes over the cervix and under the fetal presenting part, unprotected by placenta or umbilical cord. The condition usually results either from a velamentous insertion of the cord into the membranes rather than the placenta or from vessels running between lobes of a placenta with one or more accessory lobe. It is a condition which, if undiagnosed is associated with a perinatal mortality of approximately 60%. The condition is important because, when the membranes rupture, spontaneously or artificially, the fetal vessels running through the membranes have a high risk of concomitant rupture, frequently resulting in fetal exsanguination and death. The incidence of vasa previa is approximately 1 in 2,500 deliveries. Risk factors for the condition include a second-trimester low-lying placenta (even if the "low lying" placenta or placenta previa resolves in the third-trimester), pregnancies in which the placenta has accessory lobes, multiple pregnancies, and pregnancies resulting from in vitro fertilization.