Placenta previa is the implantation of the placenta over or near the internal os of the cervix. The placenta may cover the internal os completely (total previa) or partially (partial previa), or it may encroach on the internal os (low-lying placenta or marginal previa). Placenta previa occurs in 1 of 200 deliveries, usually in multiparas, in patients who have had a cesarian section, or in patients with uterine abnormalities (e.g., fibroids) that inhibit normal implantation .
Patients usually present with painless abnormal genital tract bleeding, and their first bleed usually starts in the third trimester of pregnancy. These cases usually indicate maternal or fetal compromise. Whenever a pregnant reproductive female presents with third trimester bleeding, placenta previa should always be suspected.
Diagnosis happens by ultrasound, since pelvic examination is contraindicated until the placenta can be localized. Management includes hospitalization, evaluation of the fetus and mother, placental localization, and a planned delivery.