Placenta Previa

Symptoms and Complications

Slight and occasional bleeding may occur during the first and second trimester of pregnancy. The color of the blood may be bright red and it may start and stop then restart after several days or weeks. Sudden and excessive bleeding may occur in the third trimester of pregnancy.

Bleeding is usually not accompanied by pain, although uterine cramping may occur at the time of bleeding in some women. In 7% to 30% of women there may be no bleeding at all.

The bleeding occurs because as the pregnancy progresses, the placenta gets detached from the uterine walls. In the third trimester the uterine walls become thinner and spread to accommodate the growing fetus. If placenta previa is present, the placenta is attached very low on the uterine wall. This thinning makes the placenta stretch and tear away from the uterine wall, leading to bleeding.

The following are the possible complications of placenta previa:

  • slow fetal growth due to insufficient blood supply
  • fetal anemia
  • fetal distress due to low oxygen supply
  • shock and death of the mother if the bleeding is excessive
  • infection and formation of blood clots
  • blood loss requiring transfusion

If you are diagnosed with complete placenta previa, your doctor will advise you to have a cesarean section for the delivery of your baby.

Making the Diagnosis

The condition may be diagnosed by an ultrasound showing the position of the placenta. If it is detected late in the first or early in the second trimester, often the placenta's location will shift as the uterus enlarges. This can be followed by ultrasound. Some women may even remain undiagnosed until delivery, especially in cases of marginal placenta previa. Painless bleeding from the vagina during the third trimester of pregnancy may also indicate the condition.

In many cases, a diagnosis of placenta previa in the early weeks (usually before Week 20) may correct itself as the pregnancy progresses. In other cases, placenta previa may be missed if the placenta is located behind the baby's head.

Digital (using the fingers) examination of the vagina and the cervix is avoided in cases of placenta previa, as this could cause the placenta to tear and lead to heavy bleeding.

In addition to painless vaginal bleeding, other signs that your doctor may look for to confirm a diagnosis of placenta previa include:

  • abdominal ultrasound during the second trimester showing the low placement of the placenta
  • low-lying placenta revealed by transvaginal or transperineal ultrasound

Treatment and Prevention

Placenta previa is a condition that cannot be prevented, however, if you are at high risk, do talk about this with your health care provider to avoid complications.

The treatment for placenta previa is usually aimed at minimizing symptoms and ensuring the pregnancy completes 36 weeks. The goal of this treatment is safe delivery of the fetus as close to term as possible by cesarean section. The treatment will therefore depend on answers to the following questions:

  • What is the extent or amount of abnormal bleeding?
  • How much of the placenta is covering the cervix?
  • What is the position of the fetus in the uterus?
  • Is the fetus developed enough to survive outside the uterus?
  • How many births has the mother previously had?
  • Has labor started?

Once placenta previa has been diagnosed, further bleeding and complications may be avoided by ensuring the mother has complete bed rest, sometimes in the hospital. Also, pelvic examinations or any sexual activity that may lead to irritation of the cervix or the uterine walls should be avoided.

Once the pregnancy comes to term, or if the bleeding is excessive, the baby will be delivered by cesarean section, especially in cases of complete placenta previa. Vaginal delivery for women with placenta previa might result in placental tear and hemorrhage, putting the mother and the baby at risk.

With early and more accurate diagnosis of placenta previa, this condition is no longer as big a threat to the mother and the baby as it once was. The biggest danger remains premature delivery of the baby because of the heavy bleeding.


Melanie N. Smith, MD, PhD, Department of Obstetrics and Gynecology, Brigham and Women's Hospital, Boston, MA.  Review provided by VeriMed Healthcare Network.

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The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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