After a woman gives birth and the umbilical cord has been cut, her body sends a signal to her 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 path the baby just took. Sometimes, the placenta begins to peel away from the uterus too soon, 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. Many believe, however, that tiny blood vessels on the surface of the placenta begin to leak and form a bruise or blood blister, which then spreads between the placenta and the uterine wall. The blood loosens the connection between the uterine wall and the placenta, allowing it to separate.
Types of Abruption
To decide on 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 her vagina. A woman with placental abruption always bleeds, but sometimes the blood stays within her uterus and can be seen only through an ultrasound. An abruption of this sort is called a concealed abruption. About 20% 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, while at other times the entire placenta separates. A doctor will use 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.
Diagnosing Placental Abruption
When a woman has placental abruption, the most common signs are:
- vaginal bleeding;
- abdominal tenderness or back pain;
- contractions; and
- abnormalities in the baby's heartbeat.
If a woman is already in labor, abruption can increase the duration of contractions and cause her uterus to become and remain hard to the touch.
Placental abruption is often difficult to diagnose because only about 60 to 75% of women have signs-signs that often indicate other conditions, like placenta previa, uterine rupture, and labor. Placental abruption is diagnosed clinically by close observation. Ultrasounds and certain laboratory tests may be helpful, but most cases are diagnosed by painful uterine contractions and abnormalities in the baby's heartbeat. To rule out other causes of abdominal pain, vaginal bleeding, and contractions, a combination of ultrasound and close observation are used.
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. A woman with heavy vaginal bleeding, for example, 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 woman's body in the uterus.)
What Causes Placental Abruption?
While doctors aren't sure what causes placental abruption, they are aware of some risk factors. Physical trauma to the stomach, for example, can pull the placenta off the uterine wall. Or, if too much fluid surrounds the baby ( polyhydramnios ), the mother's ?water? will break, causing her uterus to shrink rapidly from the loss of fluid. Because this change in size is so great, her body thinks 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 related directly to pregnancy (preeclampsia or toxemia);
- past pregnancies -the more pregnancies a woman has had, the greater her risk for abruption;
- past placental abruptions -if a woman has had an abruption in a past pregnancy, 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 2.5 times more likely to have an abruption severe enough to cause fetal death. The risk increases by 40% per each pack per day smoked;
- street drugs, especially amphetamines (speed) and cocaine-one out of every 10 pregnant women who use cocaine in the third trimester will have an abruption. ?Crack? cocaine poses the greatest risk; and
- preterm premature rupture of membranes -pregnant women who break their ?water? well before their 36th week are at higher risk for abruption. These women can be up to nine times more likely to have an abruption.
How Common is Placental Abruption?
Abruption is a common complication of pregnancy. About one in 20 women probably have small abruptions, but these are small enough they do not affect the mother or her baby. In fact, doctors rarely know that these abruptions exist. About one in 120 women who deliver has a larger abruption, and about one in 830 has an abruption so severe that the baby cannot survive.
Risks for the Mother
Placental abruption is a serious condition that may result in maternal death. Fortunately, 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 100 die, 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; 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. This results in additional blood loss.
There is another 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). Often, this type of uterus may not be able to contract as well and may need to be removed (hysterectomy) in order to control uterine bleeding.
Risks for the Baby
The most significant risk to the baby is dying inside the womb. The chances of this happening depend on:
- how much of the placenta has separated from the uterine wall -a doctor will use 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: the most significant consequence is a slight lack of oxygen and nutrition. Larger or complete separations almost always cause fetal death unless labor is induced; and
- how far along a woman is in her pregnancy -if an abruption is severe, often the only cure is to induce labor, regardless of how well developed the baby is. In the last weeks of pregnancy, when a baby weighs over five pounds, 98% survive. The more prematurely the baby is born, and the lower the birth weight, the higher the chance that the baby will not survive, or will suffer residual damage.