The placenta is an unborn baby's life support system. It forms from the same cells as the embryo and attaches to the wall of the uterus. The placenta forms connections with the mother's blood supply, from which it supplies oxygen and nutrients to the fetus. The placenta also connects with the fetus's blood supply, from which it removes wastes and returns them to the mother's blood. The mother's kidneys dispose of the waste.
The placenta has other important functions in pregnancy. It produces hormones that play a role in triggering labor and delivery. The placenta also helps protect the fetus from infections and potentially harmful substances. After the baby is delivered, the placenta's job is done, and it is delivered as the afterbirth.
The mature placenta is flat and circular and weighs about 1 pound. But sometimes the placenta:
- Is structured abnormally
- Is poorly positioned in the uterus
- Does not function properly
Placental problems are among the most common complications of the second half of pregnancy. Here are some of the most frequent placental problems and how they can affect mother and baby.
What is placental abruption?
Placental abruption (sometimes called abruptio placentae) is a condition in which the placenta peels away from the uterine wall, partially or almost completely, before delivery. Mild cases may cause few problems, but severe cases can deprive the fetus of oxygen and nutrients. Severe cases also can cause bleeding in the mother that can endanger both her and the baby.
Placental abruption increases the risk of premature birth (birth before 37 completed weeks gestation). Studies suggest that abruption contributes to about 10 percent of premature births (1). Premature babies are at increased risk for health problems during the newborn period, lasting disabilities and even death. Abruption also increases the risk for poor fetal growth and stillbirth (1).
How common is placental abruption?
Abruption occurs in about 1 in 100 pregnancies (2). It occurs most often in the third trimester, but it can happen any time after about 20 weeks of pregnancy.
What are the symptoms of abruption?
The main sign of placental abruption is vaginal bleeding. A pregnant woman should contact her health care provider if she has vaginal bleeding.
The pregnant woman also may experience uterine discomfort and tenderness or sudden, continuous abdominal pain. In a few cases, these symptoms may occur without vaginal bleeding because the blood is trapped behind the placenta.
How is placental abruption diagnosed?
If the health care provider suspects an abruption, she probably will recommend that the woman go to the hospital for a complete evaluation. The provider will do a physical examination and, most likely, an ultrasound examination. An ultrasound can detect many, but not all, cases of abruption.
How is placental abruption treated?
How a woman is treated depends on the severity of the abruption and her stage of pregnancy.
A mild abruption usually is not dangerous unless it progresses. If a woman has a mild abruption at term, her health care provider may recommend prompt delivery (either by inducing labor or by c-section) to avoid any risks associated with a worsening abruption.
If a woman has a mild abruption and her fetus would be very premature if delivered immediately, her provider will probably admit her to the hospital for careful monitoring. If tests show that neither mother nor baby is having difficulties, the provider may try to prolong the pregnancy to avoid prematurity-related complications for the baby.
If the provider suspects that the abruption is likely to result in premature delivery between 24 and 34 weeks of pregnancy, she will probably recommend treatment with drugs called corticosteroids. These drugs speed maturation of the fetal lungs and significantly reduce the risk of prematurity-related complications and infant deaths.
Some women with mild abruptions may be able to go home after the bleeding stops, while others may need to stay in the hospital until delivery (1).
If an abruption progresses, a woman is bleeding heavily, or the baby is having difficulties, a prompt delivery, usually by c-section, probably will be necessary.
What causes placental abruption?
The cause of abruption is unknown. However, the following factors can increase a woman's risk for abruption (1, 3):
What is the risk of an abruption happening again in another pregnancy?
A woman who has had an abruption has about a 10 percent chance of it happening again in a later pregnancy (1).
What can a woman do to reduce her risk for abruption?
In most cases, abruption cannot be prevented. However, these steps may help a woman reduce her risk:
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Keep high blood pressure under control. Women who have high blood pressure should see their health care provider regularly and take medication, if recommended. Women who are not yet pregnant should see their provider for a preconception checkup to get their blood pressure under control right from the start.
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Avoid cigarettes and cocaine. These contribute to abruption and other pregnancy complications.
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Wear a seat belt. This can help prevent trauma resulting from auto accidents.
- Discuss possible treatments for blood clotting disorders with a health care provider. Some women with inherited blood clotting disorders may benefit from treatment, for example with blood-thinning drugs, during pregnancy (1). Some providers recommend treatment to affected women who have had an abruption or other pregnancy complication that may be linked with a blood-clotting disorder.
What is placenta previa?
Placenta previa is a low-lying placenta that covers part or all of the opening of the cervix. This positioning of the placenta can block the baby's exit from the uterus. As the cervix begins to thin and dilate in preparation for labor, blood vessels that connect the abnormally placed placenta to the uterus may tear, resulting in bleeding. During labor and delivery, bleeding can be severe, endangering mother and baby.
As with placental abruption, placenta previa can result in the birth of a premature baby.
How common is placenta previa?
Placenta previa occurs in about 1 in 200 pregnancies (4).
What are the symptoms of placenta previa?
The most common symptom of placenta previa is painless uterine bleeding during the second half of pregnancy. Women who experience vaginal bleeding in pregnancy should contact their health care provider.
How is placenta previa diagnosed?
An ultrasound examination can diagnose placenta previa and pinpoint the placenta's location. The provider usually avoids doing a vaginal examination when placenta previa is suspected because the examination may trigger heavy bleeding.
Some women who have not experienced vaginal bleeding learn during a routine ultrasound examination that they have a low-lying placenta. A pregnant woman should not be too worried if this happens to her, especially if she is in the first half of pregnancy. More than 90 percent of the time, placenta previa diagnosed in the second trimester corrects itself by term (3, 4).
How is placenta previa treated?
How a woman with placenta previa is treated depends on her stage of pregnancy, the severity of the bleeding and the condition of mother and baby. The goal, whenever possible, is to prolong pregnancy until the baby is at or near full term. Cesarean delivery is recommended for nearly all women with placenta previa because c-sections usually can prevent severe bleeding.
When a woman develops significant bleeding due to placenta previa after about 34 weeks of pregnancy, her provider may recommend a prompt c-section. Babies born after this time usually do well, though some have mild prematurity-related health problems during the newborn period.
Women who develop bleeding as a result of placenta previa before about 34 weeks are generally admitted to the hospital, where they can be monitored closely. If tests show that mother and baby are doing well, the provider will probably attempt to prolong the pregnancy. In some cases, when there has been a significant amount of bleeding, the mother may be treated with blood transfusions. She also will be treated with corticosteroid drugs if she is likely to deliver before 34 weeks.
Some women are able to go home after bleeding stops, but others must remain in the hospital until delivery. At 36 to 37 weeks, if she hasn't delivered, the provider may suggest a test of the amniotic fluid (obtained by amniocentesis) to see if the baby's lungs are mature. If they are, the provider will likely recommend a c-section at that time to prevent risks associated with any future bleeding episodes.
At any stage of pregnancy, a prompt c-section may be necessary if the mother develops dangerously heavy bleeding, or if mother or baby is having difficulties.
What causes placenta previa?
The cause of placenta previa is unknown. However, certain factors can increase a woman's risk (3, 4):
- Cigarette smoking
- Cocaine use
- Being more than 35 years of age
- Second or later pregnancy
- Previous uterine surgery, including a c-section; a D&C (dilation and curettage, in which the lining of the uterus is scraped), which is often done following a miscarriage or during an abortion
- Pregnant with twins, triplets or more
What is the risk of placenta previa happening again in another pregnancy?
A woman who has had a placenta previa in a previous pregnancy has a 2 to 3 percent chance of a recurrence (3).
Can a woman reduce her risk for placenta previa?
There is no way to prevent placenta previa. However, a woman may be able to reduce her risk by avoiding using cigarettes and cocaine. She also may be able to reduce her risk in future pregnancies by avoiding having an elective c-section (i.e., a c-section scheduled for convenience), unless there is a medical reason.
What is placenta accreta?
Placenta accreta refers to a placenta that implants too deeply and too firmly into the uterine wall. Similarly, placenta increta and percreta refer to a placenta that imbeds itself even more deeply into uterine muscle or through the entire thickness of the uterus, sometimes extending into nearby structures, such as the bladder.
How common are placenta accreta and related disorders?
These disorders occur in about 1 in 2,500 deliveries (4). They sometimes lead to the birth of a premature baby.
What are the symptoms of placenta accreta and related disorders?
Like placenta previa, these disorders often cause vaginal bleeding in the third trimester.
Who is at risk for placenta accreta and related disorders?
These disorders occur most frequently in women who have placenta previa in the current pregnancy and also have a history of one or more c-sections or other uterine surgery (4).
How are placenta accreta and related disorders diagnosed?
These disorders can be diagnosed with an ultrasound examination. In some cases, another imaging technique called magnetic resonance imaging (MRI) may be recommended (4).
How are placenta accreta and related disorders treated?
In these disorders, the placenta does not completely separate from the uterus as it should following the delivery of the baby. This can lead to dangerous hemorrhage following vaginal delivery. The placenta usually must be surgically removed to stop the bleeding, and often a hysterectomy (removal of the uterus) is necessary.
When placenta accreta is diagnosed before birth, a c-section immediately followed by a hysterectomy may be planned in order to reduce blood loss and complications in the mother. In some cases, other surgical procedures can be used to save the uterus.
What are some other placental problems?
In some cases the placenta may not develop correctly or function as well as it should. It may be too thin, too thick or have an extra lobe, or the membranes may be improperly attached. Or problems can occur during pregnancy that damage the placenta, including infections, blood clots and areas of tissue destruction (infarcts). These placental abnormalities can contribute to a number of complications, such as miscarriage, poor fetal growth, prematurity, maternal hemorrhage at delivery and, possibly, birth defects. A doctor often will examine the placenta following delivery or send it to the laboratory, especially if the newborn has certain complications, such as poor growth, to help diagnose the cause of the problem.
Does the March of Dimes support research on placental conditions?
March of Dimes grantees are studying how certain infections, such as cytomegalovirus (CMV), may damage the placenta, possibly contributing to miscarriage, poor fetal growth and birth defects, such as cerebral palsy.
Others are exploring how certain genes regulate the development and function of the placenta in order to develop ways to prevent miscarriages, growth problems and premature births, which may result from placental abnormalities.
References
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Oyelese, Y. and Ananth, C.V. Placental Abruption. Obstetrics and Gynecology, volume 108, number 4, October 2006, pages 1005-1016.
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Ananth, C.V., et al. Placental Abruption in Term and Preterm Gestations. Obstetrics and Gynecology, volume 107, number 4, April 2006, pages 785-792.
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Kay, H.H. Placenta Previa and Abruption, in Scott, J.R., et al. (eds.): Danforth's Obstetrics and Gynecology, Ninth Edition, Philadelphia, Lippincott Williams & Wilkins, 2003, pages 365-379.
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Oyelese, Y. and Smulian, J.C. Placenta Previa, Placenta Accreta, and Vasa Previa. Obstetrics and Gynecology, volume 107, number 4, April 2006, pages 927-941.
March 2007
