Placenta previa.

Placenta previa occurs in approximately one in 200 pregnancies. The cause is unknown, but endometrial damage due to prior pregnancy, cesarean section, and other factors predispose to it. Diagnosis is usually made by transabdominal ultrasonography. False-positive diagnoses are common in the second trimester and the term "potential placenta previa" has been proposed to describe this situation. Bleeding with placenta previa is usually associated with uterine contractions, thus the introduction of tocolysis. Placenta accreta is common in the patient with one or more previous cesarean sections and placenta previa in the current pregnancy. Management of placenta previa is expectant and involves avoidance of digital vaginal examination, delay of delivery until 36 weeks' gestation and/or documented fetal lung maturity, transfusion support to maintain maternal hematocrit greater than or equal to 30%, serial ultrasonography, antepartum fetal heart rate monitoring, glucocorticoids, tocolytic therapy, and elective delivery by cesarean section. Maternal mortality is rare with placenta previa. Perinatal mortality is currently 4% to 8% primarily related to complications of prematurity.