RELATED STORIES • Premature birth • Preeclampsia • Ectopic pregnancy • Placenta previa

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The placenta is a structure that develops in the uterus during pregnancy to nourish the growing baby. If the placenta separates from the inner wall of the uterus before delivery, it's known as placental abruption. This rare — but serious — complication of pregnancy requires immediate medical attention.

With placental abruption, the uterus bleeds from the site where the placenta was attached. The blood typically passes through the cervix and out the vagina. Sometimes, however, the blood remains trapped behind the placenta. Left untreated, placental abruption puts both mother and baby in jeopardy.

Placental abruption is most common in the third trimester, but it can begin any time after 20 weeks of pregnancy. With close monitoring and delivery at the appropriate time, the outlook is promising.

In the early stages of placental abruption, you may not have any signs or symptoms.

Bleeding from the vagina is often the first sign. The amount of bleeding can vary greatly — and the amount of blood doesn't necessarily correspond to how much of the placenta has separated from the inner wall of the uterus.

Other signs and symptoms of placental abruption may include:

• Abdominal pain
• Back pain
• Uterine tenderness
• Rapid uterine contractions

If you experience any of these signs or symptoms, contact your health care provider right away or seek emergency care.

The exact cause of placental abruption is often unknown.

Rarely, trauma or injury to the abdomen — from an auto accident or fall, for example — causes placental abruption. In other rare cases, placental abruption is caused by an unusually short umbilical cord or rapid loss of amniotic fluid, the fluid that surrounds and protects the baby in the uterus.

High blood pressure (hypertension) in pregnancy is the most common condition associated with placental abruption. That's true whether the high blood pressure first developed during pregnancy or was present before conception. Maternal blood-clotting disorders also increase the risk of placental abruption.

Placental abruption appears to be more common in women older than 40 and those who have:

• Diabetes
• A multiple pregnancy
• An unusually large amount of amniotic fluid
• Numerous previous deliveries

Lifestyle factors play a role as well. Placental abruption is more common in women who smoke and those who abuse alcohol and drugs such as cocaine during pregnancy.

If you experience placental abruption, there's at least a 10 percent chance that the condition will recur in a subsequent pregnancy. After two episodes of placental abruption, the chance of recurrence increases to more than 20 percent.

If you have placental abruption, prompt treatment is essential. Contact your health care provider right away or seek emergency care if you experience signs or symptoms of placental abruption, including:

• Vaginal bleeding
• New back pain
• Abdominal pain
• Rapid uterine contractions, often coming one right after another

If your health care provider suspects placental abruption, he or she will check for uterine tenderness or rigidity. Your health care provider may do blood tests or an ultrasound to help identify possible sources of bleeding. Diagnosis is based on the overall clinical circumstances. Often, placental abruption can't be confirmed until after delivery — when the placenta is delivered with an attached blood clot.

Placental abruption can cause life-threatening problems for you and your baby. Without prompt treatment, maternal blood loss may lead to shock. Your baby may be deprived of oxygen and nutrients. Sometimes, decreased oxygen to the brain leads to later neurological or behavioral problems. In severe cases, the baby may not survive.

Blood loss may be a concern after delivery, too. If bleeding from the site of the placental attachment can't be controlled after the baby is born, emergency removal of the uterus (hysterectomy) may be needed.

If your health care provider suspects placental abruption, treatment depends on your condition, the baby's condition and the stage of the pregnancy.

If the abruption seems mild, if your baby's heart rate is normal, and if it's too soon for the baby to be born, you may be hospitalized for close monitoring. If the bleeding stops and your baby's condition is stable, your health care provider may prescribe bed rest at home. In some circumstances, you may be given medication to help your baby's lungs mature — in case early delivery becomes necessary.

If you're 36 weeks or more into your pregnancy and placental abruption is minimal, a closely monitored vaginal delivery may be possible. If the abruption progresses or jeopardizes your health or your baby's health, you'll need an immediate delivery — usually by Caesarean section. If you experience severe bleeding, you may need a blood transfusion.

You can't prevent placental abruption — but you can decrease certain risk factors. Don't drink alcohol, smoke or take illicit drugs during pregnancy. If you have high blood pressure or diabetes, work with your health care provider to control your condition.

If you've had a placental abruption, talk to your health care provider before conceiving again. When you become pregnant, your health care provider will carefully monitor your condition to make sure your pregnancy is progressing normally.