praevia

Praevia, in obstetrics commonly called placenta previa, is a condition in which the placenta implants in the lower part of the uterus near or over the internal cervical os. It can cause painless vaginal bleeding in the second or third trimester and may threaten both mother and fetus during delivery.

Placenta praevia is categorized by the placenta's relation to the internal os: complete previa (the placenta covers the os completely); partial previa (the placenta covers part of the os); marginal previa (the placental edge reaches the os but does not cover); and low-lying placenta (implantation in the lower uterus near the os without covering). The diagnosis is usually made by ultrasound, with transvaginal ultrasound providing the most accurate assessment.

Most bleeding episodes are painless and occur in the third trimester. Diagnosis is by ultrasound; MRI is used in uncertain cases. Management depends on gestational age, bleeding, and fetal status. If bleeding is mild and the placenta is low-lying or non-covering, expectant management with activity modification and planned cesarean delivery around 36–37 weeks may be appropriate. Heavy bleeding or term previa typically requires cesarean delivery. Digital vaginal examination should be avoided to reduce hemorrhage risk, and the patient should be managed in a setting equipped for maternal-fetal emergencies.

Complications include antepartum hemorrhage, preterm birth, fetal growth restriction, malpresentation, and placenta accreta, especially after prior uterine surgery. The condition contributes to obstetric hemorrhage, but outcomes have improved with prenatal imaging and planned cesarean delivery in modern care.