It usually happens in the third trimester but it can happen any time after 20 weeks of pregnancy. Mild cases may cause few problems. An abruption is mild if only a very small part of the placenta separates from the uterus wall.

How early can placental abruption occur?

Placental Abruption Signs and Symptoms

Placental abruption affects about 1% of pregnant woman. It can occur at any time after 20 weeks of pregnancy, but it's most common in the third trimester. When it happens, it's usually sudden. You might notice vaginal bleeding, but there might not be any.

What is the most common cause of placental abruption?

The cause of placental abruption is often unknown. Possible causes include trauma or injury to the abdomen — from an auto accident or fall, for example — or rapid loss of the fluid that surrounds and cushions the baby in the uterus (amniotic fluid).