Placental abruption is caused by the premature separation of the placenta from the wall of the uterus. Placental abruption is seen in the third trimester of pregnancy, after 25 weeks gestation. When this problem occurs, it is considered an emergency. The incidence of placental abruption in the US is less than 1 percent.

Risk factors for placental abruption include:

• Placental abruption in the past
• Alcohol use
• Smoking
• Drug abuse
• Aspirin use during pregnancy