Placenta previa and antepartum hemorrhage after previous cesarean section.

A prospective study was conducted to determine the risk of placenta previa and unexplained antepartum hemorrhage after a previous cesarean section (CS). Of a total of 24,644 patients, 81 (0.33%) had a placenta previa which demanded abdominal delivery. The risk of placenta previa was 0.25% with an unscarred uterus and 1.22% in patients with one or more previous CS (the difference was statistically significant p less than 0.001). The corresponding figures for unexplained antepartum hemorrhage were 0.40% and 3.81%, respectively (p less than 0.001). Patients presenting with a placenta previa and a scarred uterus had a 16% risk of undergoing cesarean hysterectomy because of placenta accreta and severe hemorrhage compared to 3.6% in patients with placenta previa and an unscarred uterus. In conclusion, cesarean deliveries predispose to placenta previa, placenta accreta and antepartum hemorrhage during subsequent pregnancies. This relationship has to be considered in the cost-benefit equation for decision of route of delivery.