Placenta Previa

Placenta previa occurs when implantation of the placenta is low in the uterus; it is either overlying or encroaching on the cervical os. Placenta previa is present in approximately 0.6% of all pregnancies. It may be categorized as "total" if the placenta completely covers the os, "partial" if there is some encroachment on the os by the placenta, and "marginal" if the placenta is not covering but is close to the internal os ( Fig. 58-17 ). The condition is more common in multiparous women, and it is especially common in women who have had a previous cesarean section. Typically, in contrast to placental abruption, placenta previa is characterized by painless vaginal bleeding in the third trimester. Bleeding may stop spontaneously, in which case conservative management is recommended. However, if bleeding persists, stabilization of the mother and delivery of the fetus may be required.