Although sudden massive bleeding during pregnancy may occur in patients with placenta previa, regardless of the pres- ence or absence of any abnormal ultrasonographic findings, a short uterine cervical length in the third trimester and sinus venosus at the margin of the placenta may predict an increased risk of antenatal bleeding in pregnant women demonstrating placenta previa.
During a Cesarean section, advanced maternal age, a history of a previous Cesarean section, and the presence of sponge-like findings, are risk factors for massive bleeding in patients with placenta previa, regardless of the existence of placental adherence. The ultrasound findings of a placenta located on the previous Cesarean section wound, and a lack of a clear zone, are serious risk factors for placental adherence.