Placental abruption is most likely to occur in the last trimester of pregnancy, especially in the last few weeks before birth. Signs and symptoms of placental abruption include:

• Vaginal bleeding
• Abdominal pain
• Back pain
• Uterine tenderness
• Uterine contractions, often coming one right after another
• Firmness in the uterus or abdomen

Abdominal pain and back pain often begin suddenly. The amount of vaginal bleeding can vary greatly, and doesn't necessarily correspond to how much of the placenta has separated from the uterus. It's possible for the blood to become trapped inside the uterus, so even with a severe placental abruption, there might be no visible bleeding.

In some cases, placental abruption develops slowly (chronic abruption), which can cause light, intermittent vaginal bleeding. Your baby might not grow as quickly as expected, and you might have low amniotic fluid (oligohydramnios) or other complications.

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).

Factors that can increase the risk of placental abruption include:

• Placental abruption in a previous pregnancy, unless the abruption was caused by abdominal trauma, assuming the trauma isn't repeated in the current pregnancy
• Chronic high blood pressure (hypertension)
• High blood pressure during pregnancy, resulting in preeclampsia or eclampsia
• A fall or other type of blow to the abdomen
• Smoking
• Cocaine use during pregnancy
• Early rupture of membranes, which causes leaking amniotic fluid before the end of pregnancy
• Infection inside of the uterus during pregnancy (chorioamnionitis)
• Carrying more than one baby
• Being older, especially after age 40

Placental abruption can cause life-threatening problems for both mother and baby.

For the mother, placental abruption can lead to:

• Shock due to blood loss
• Blood clotting problems (disseminated intravascular coagulation)
• The need for a blood transfusion
• Failure of the kidneys or other organs resulting from significant blood loss
• Rarely, when uterine bleeding cannot be controlled, hysterectomy may be necessary

For the baby, placental abruption can lead to:

• Restricted growth from not getting enough nutrients
• Not getting enough oxygen
• Premature birth
• Stillbirth