Placenta abruptio is the separation of the placenta from the uterus before a baby is delivered, typically in the third trimester of pregnancy but sometimes earlier. This can lead to preterm birth, low birth weight [at or below 2500 g (5.51 lb)], and major maternal blood loss.

Since the placenta delivers oxygen and nutrients from the mother's bloodstream to the fetus and carries waste products away from the fetus, placenta abruptio can be life-threatening for a mother (from severe bleeding), her fetus, or both.

Separation of the placenta from the uterus may be partial or complete. A partial separation may cause only minor bleeding and not endanger the lives of the fetus or mother. In rare cases, a complete separation may lead to fetal death and severe bleeding that can endanger the mother's life.

Symptoms of placenta abruptio can include light or heavy vaginal bleeding, uterine tenderness or pain, or signs of preterm labor. A pregnant woman with any of these symptoms must seek emergency medical attention.

Certain factors increase the risk of placenta abruptio, including high blood pressure, a previous placenta abruptio, smoking or drug use while pregnant, injury to the abdomen, multiple pregnancy, a blood-clotting disorder, and a fibroid or scar tissue on the uterus where the placenta grows.