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Complications of the Placenta

The placenta provides important nutrients to the developing baby, and therefore is crucial to the baby’s development. Usually, pregnancy proceeds without complication. Sometimes, however, problems can arise. Complications of the placenta can be very serious, and can cause concerns for both mother and baby.

Placental insufficiency

Placental insufficiency is the failure of the placenta to provide enough nutrients to the unborn baby during pregnancy. This is caused by a failure of the placenta to grow or function properly, and it can result in fetal growth restriction and low birth weight. There are no known symptoms of placental insufficiency, but the unborn baby may move less frequently than expected. Fetal growth restriction can be detected by the health care provider when she measures the height of the top of the uterus, called the fundus, during regular medical visits. The condition and size of the placenta, and the health of the baby, can also be monitored using ultrasound.

Infarcts in the placenta

There may be areas of dead tissue, called infarcts, within the placenta that result in reduced blood flow in those areas. These infarcts are often caused by a problem with the vessels within the placenta. Severe pregnancy-induced hypertension is known to increase the number of infarcts within the placenta. Usually, infarcts in the placenta will not affect the unborn baby. However, in certain cases and especially in women with severe hypertension, the reduced blood flow in the placenta may be enough to cause poor growth and even death of the unborn baby.

Placenta previa

The placenta usually implants and grows in the upper part of the uterus. In 0.5% to 1% of pregnancies, however, the placenta will implant in the lower part of the uterus, blocking the cervix, which is the opening from the uterus to the vagina. This condition is more common in black women, other minorities, older women, cigarette smokers, and women who have had previous caesarean sections or abortions.

Placenta previa is usually diagnosed through the use of ultrasound. If the cervix is completely blocked, the baby cannot be born vaginally, and will need to be delivered by caesarean section. If the cervix is only marginally blocked during pregnancy, there is a chance that when the uterus grows, the edge of the placenta will become farther away from the cervix so labour can proceed safely. If not, a caesarean section is recommended.

Complete Placenta Previa
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The placenta is normally located in the upper part of the uterus. With complete placenta previa, the placenta implants in the bottom part off the uterus and blocks the cervix. The baby will need to be delivered by caesarean section.
 

Marginal Placenta Previa
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The placenta is normally located in the upper part of the uterus. With marginal placenta previa, the placenta implants near the bottom part off the uterus and may block part of the cervix. The baby may need to be delivered by caesarean section.
Placenta previa is a common cause of bleeding during late pregnancy. In the second trimester, the bleeding should stop with bed rest, either at home or in the hospital. If you have bleeding in the second trimester that does not stop, you will be monitored in hospital and possibly given blood transfusions. If your bleeding continues or recurs, you may need to monitored in the hospital until the unborn baby is of an age where he can survive outside the womb. If your bleeding stops, you may be discharged from the hospital to continue bed rest at home.

In the third trimester, monitoring continues. If your bleeding is significant and continues past 34 weeks of pregnancy, your doctor may decide to go ahead with a caesarean section. In trimester three, some women with placenta previa have a number of small bleeding episodes followed by one massive bleed which requires immediate surgical delivery to prevent death of the baby. Placenta previa is associated with higher rates of premature birth and therefore low birth weight, as well as respiratory distress syndrome and anemia in the baby. Placenta previa without bleeding does not seem to affect the baby’s likelihood of surviving childbirth.

Placental abruption

Placental abruption is a condition where a part of the placenta separates from the uterus during pregnancy. There are many blood vessels within the placenta that transfer nutrients from the mother to the unborn baby. If the placenta detaches during pregnancy, these blood vessels break, and thus there is bleeding. The larger the area that detaches, the more bleeding there is.

Placental Abruption
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The placenta is normally implanted into the wall of the uterus where there are many blood vessels that supply the baby with oxygen and nutrients. With placental abruption, the placenta becomes detatched from the uterus, and bleeding may occur.
Like placenta previa, the incidence of placental abruption is about 0.5% to 1%. However, in contrast to placenta previa, placental abruption is a leading cause of death for unborn and newborn babies. This is because the breakage of blood vessels reduces the oxygen supply to the unborn baby. Placental abruption is also associated with high rates of premature birth and fetal growth restriction.

The symptoms of placental abruption include:

  • vaginal bleeding
  • pain in the uterus
  • contractions of the uterus that do not stop
  • abnormalities of the fetal heart rate

Placental abruption is diagnosed through an assessment of symptoms. If you have only mild bleeding due to an abruption in pregnancy, you may be admitted to hospital for surveillance. You may need some blood tests, and the unborn baby will be monitored. If your bleeding and other symptoms stop, you may be discharged from hospital and advised to take bed rest. If, on the other hand, your bleeding is heavy, you may need to have an emergency caesarean section.

Some women are more prone to developing placental abruption. Risk factors for placental abruption are as follows:

  • history of abruption in a previous pregnancy
  • abdominal trauma from domestic abuse or a motor vehicle accident
  • uterine defects such as tumours
  • maternal diseases such as hypertension and pregnancy-induced hypertension
  • cigarette smoking
  • cocaine use
  • an abnormality called circumvallate placenta, where the placenta is thickened and spread over a smaller surface area along the uterine lining

If you have a placental abruption during pregnancy, there is a 25% chance of it recurring in a subsequent pregnancy. Therefore, in future pregnancies, you will be monitored closely starting from two weeks before the gestational age at which the previous abruption occurred. For example, if you have an abruption at 34 weeks in this pregnancy, you will be closely monitored in subsequent pregnancies from week 32 onwards. Monitoring will include a series of ultrasounds to check for fetal growth restriction and placental bleeding.

Placenta accreta

This is when the placenta grows too deeply into the inner wall of the uterus. The placenta becomes so firmly attached to the uterus that it will not properly separate from the uterus after the baby is born. Placenta accreta is most common in women who have uterine scarring from previous deliveries or surgeries such as caesarean section.

Placenta accreta causes excessive bleeding after childbirth. Usually the placenta must be removed surgically to stop the bleeding. If the bleeding cannot be stopped in this way, the entire uterus may need to be removed.

Nicolette Caccia, MEd, MD, FRCSC

Rory Windrim, MB, MSc, FRCSC

9/11/2009




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