Pregnancy Complications: Placental Abruption Health Article

After a woman gives birth and the umbilical cord has been cut, her body sends a signal to the uterus that the placenta is no longer needed. The placenta then begins to peel away from the uterine wall so that it can leave the body, following the same path as the recently delivered baby. Sometimes, however, the placenta begins to peel away from the uterus early, while the baby still needs the placenta to supply oxygen and nutrients. This is called placental abruption, or just abruption.

Doctors aren't sure exactly how placental abruption occurs. However, many believe that tiny blood vessels on the surface of the placenta begin to leak, forming a bruise or blood blister that then spreads between the placenta and the uterine wall. This loosens the connection between the uterine wall and the placenta, allowing it to separate.

Types of Abruption

To determine the type of abruption a woman has, doctors look for two things:

• whether the blood remains inside a woman's uterus or flows out through the vagina. A woman with placental abruption always bleeds, but sometimes the blood stays within her uterus and can be seen only by ultrasound. An abruption of this sort is called a concealed abruption. About 25 to 33% of abruptions are concealed; and
• the amount of placenta that has broken away from the uterine wall. Sometimes just a small part of the placenta breaks away, and other times, the entire placenta has detached. A doctor uses a percentage-anywhere from 10 to 100%-to indicate how much of the placenta has separated. The more the placenta has separated, the greater the risk to the mother and her baby.

How Common Is Placental Abruption?

Abruption is a common complication of pregnancy. About one in 20 pregnant women probably have small abruptions, but these are so small that they don't affect the mother or her baby. In fact, doctors rarely know that these abruptions happen. About one in 120 pregnant women who deliver has a larger abruption, and about one in 800 has an abruption so severe that the baby cannot survive.

What Causes Placental Abruption?

While doctors aren't sure what causes placental abruption, they are aware of some of the risk factors. Physical trauma to the stomach, for example, can cause the placenta to separate from the uterine wall. Alternately, if too much fluid surrounds the baby (polyhydramnios), the mother's water can break, causing her uterus to shrink rapidly from the loss of fluid. Because this change in size is so great, her body thinks that the baby has been delivered and gives the placenta the signal to begin separating.

Factors that increase a woman's risk for abruption include:

• high blood pressure-Blood pressure problems may be unrelated to pregnancy (chronic hypertension) or directly related to pregnancy (toxemia or pre-eclampsia);
• previous pregnancies-The more pregnancies a woman has had, the greater her risk for abruption;
• previous placental abruptions-If a woman has experienced abruption in the past, she has a one in 10 chance of having one again. If she's had two or more abruptions, her chances increase to one in four;
• smoking-Women who smoke are 40% more likely than non-smokers or former smokers to have placental abruption; and
• street drugs, especially amphetamines (speed) and cocaine-One out of every 10 pregnant women who use cocaine has signs of an abruption. "Crack" cocaine poses the greatest risk.

Diagnosing Placental Abruption

When a woman has placental abruption, the most common signs are:

• vaginal bleeding;
• abdominal tenderness or back pain; and
• abnormalities in the baby's heartbeat.

If a woman is already in labor, abruption can increase contractions and cause her uterus to become hard to the touch.

Placental abruption is often difficult to diagnose, however, because only about 60 to 75% of women have signs-the same signs that often indicate other conditions, like placenta previa. (For more information about placenta previa, see Pregnancy Complications: Placenta Previa.) Placental abruption is called a "diagnosis of exclusion," which means that the doctor must systematically rule out other conditions before he or she can be sure that you have an abruption. To rule out other causes, the doctor will probably use a combination of ultrasound and close observation.

Even after a diagnosis has been confirmed, it may be difficult to determine just how much of the placenta has separated from the uterine wall. For example, a woman with heavy vaginal bleeding may have only a small amount of separation, while a woman with no bleeding at all can have complete separation (in these cases, the blood usually has been trapped inside the uterus).

Risks for the Mother

Placental abruption is a serious condition that can result in maternal death. Fortunately, though, this risk is much lower today than it was in the past. In the early-1900s, about one out of 12 women with placental abruption died. Now, less than one woman in a hundred dies, due to better surgical care, ways to make up for lost blood, antibiotics, and better hospital intensive care units (ICUs).

The main risks associated with placental abruption include:

• heavy bleeding-The amount of bleeding depends on how much of the placenta has separated from the uterine wall. The more separation that occurs, the greater the amount of bleeding. (For more information about the consequences of heavy bleeding, see Pregnancy Complications: Long-Term Consequences); and
• disruption in the blood's ability to clot (disseminated intravascular coagulation, or DIC)-DIC occurs as a complication of serious illness or heavy blood loss. DIC is a serious condition because once the clotting mechanisms of the blood have been disrupted, it is difficult to get them working again and a woman can then lose even more blood.

There is another, less serious, complication of placental abruption. Sometimes the bleeding between the placenta and the uterus spreads to the surface of the uterus, making it look purplish or blue, like a bruise. This is called uteroplacental apoplexy (or sometimes Couvelaire uterus, after the doctor who first described it). In the past, doctors would surgically remove a uterus in this condition. It is now known that while a uterus in this condition may be sore for a while, it eventually heals and does not require treatment. In some cases, however, a Couvelaire uterus may develop at the same time as DIC. If this happens, a hysterectomy may be needed to stop the bleeding.

Risks for the Baby

The most significant risk to the baby is death inside the womb. The chances of this happening depend on:

• how much of the placenta has separated from the uterine wall-A doctor uses a percentage-anywhere from 10 to 100%-to indicate how much of the placenta has separated from the uterine wall. Small separations from the uterine wall seldom harm the baby, causing only slight lack of oxygen and nutrition. Larger or complete separations almost always cause fetal death, unless the baby is delivered immediately; and
• how far along a woman is in her pregnancy-When abruption is severe, often the only cure is to deliver, regardless of how well developed the baby is. When this happens during the last weeks of pregnancy (when a baby weighs over five pounds), 98% of these infants survive. If a large or incomplete abruption happens earlier than that, when babies are smaller, there is about a 25% chance that the baby will not survive. Of the babies that do survive, up to 80% may suffer inhibited growth.

For information about treating placental abruption, go to Pregnancy Complications: Treatment of Placental Abruption.