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Placenta previa

Definition

Placenta previa is a complication of pregnancy in which the placenta grows in the lowest part of the womb (uterus) and covers all or part of the opening to the cervix.

The placenta grows during pregnancy and feeds the developing baby. The cervix is the opening to the birth canal.

Causes, incidence, and risk factors

During pregnancy, the placenta moves as the womb stretches and grows. It is very common for the placenta to be low in the womb in early pregnancy. But as the pregnancy continues, the placenta moves to the top of the womb. By the third trimester, the placenta should be near the top of the womb, so the cervix is open for delivery.

Sometimes, the placenta partly or completely covers the cervix. This is called a previa.

There are different forms of placenta previa:

  • Marginal: The placenta is next to cervix but does not cover the opening.
  • Partial: The placenta covers part of the cervical opening.
  • Complete: The placenta covers all of the cervical opening.

Placenta previa occurs in 1 out of 200 pregnancies. It is more common in women who have:

  • Abnormally developed uterus
  • Large or abnormal placenta
  • Many previous pregnancies
  • Multiple pregnancy (twins, triplets, etc.)
  • Scarring on the lining of the uterus, due to surgery, c-section, previous pregnancy, or abortion

Women who smoke or have their children at an older age may also have an increased risk.

Symptoms

The main symptom of placenta previa is sudden bleeding from the vagina. Some women have cramps, too. The bleeding often starts near the end of the second trimester or beginning of the third trimester.

Bleeding may be severe. It may stop on its own but can start again days or weeks later.

Labor sometimes starts within several days of heavy bleeding. Sometimes, bleeding may not occur until after labor starts.

See: Vaginal bleeding in pregnancy

Signs and tests

Your health care provider can diagnose this condition with a pregnancy ultrasound.

Treatment

Treatment depends on:

  • The amount of bleeding
  • Whether the baby is developed enough to survive if delivered
  • How much of the cervix is covered
  • The baby's position
  • The number of previous births you have had
  • Whether you are in labor

If the placenta is near or covering a part of the cervix, your doctor may recommend:

  • Reducing your activities
  • Bed rest
  • Pelvic rest, which means no sex, no tampons, and no douching

Nothing should be placed in the vagina.

You may need to stay in the hospital so your health care team can closely monitor you and your baby.

If you have lost a lot of blood, you may receive:

  • Blood transfusions
  • Medicines to prevent early labor
  • Medicines to help pregnancy continue to at least 36 weeks
  • Shot of special medicine called Rhogam if your blood type is Rh-negative
  • Steroid shots to help the baby's lungs mature

Your health care providers will carefully consider the risk of bleeding against early delivery of your baby. After 36 weeks, delivery of the baby may be the best treatment.

An emergency c-section may be done if the bleeding is heavy and cannot be controlled.

Nearly all women with placenta previa need a c-section. If the placenta covers all or part of the cervix, a vaginal delivery can cause severe bleeding. This can be deadly to the mother and baby.

Expectations (prognosis)

Women with placenta previa need to be carefully monitored by a health care provider. Careful monitoring and delivery by c-section help prevent most complications.

The biggest risk is severe bleeding that can be life threatening to the mother and baby. If you have severe bleeding, you baby may need to be delivered early, before major organs, such as the lungs, have developed.

Complications

Risks to the mother include:

  • Major bleeding (hemorrhage)
  • Shock
  • Death

Other risks include:

  • Blood clots
  • Infection
  • Need for blood transfusions

Risks to the baby include:

  • Blood loss in the baby
  • Death

Most infant deaths due to placenta previa occur when the baby is delivered before 36 weeks of pregnancy.

Calling your health care provider

Call your health care provider if you have vaginal bleeding during pregnancy. Placenta previa can be dangerous to both you and your baby.

References

Francois KE, Foley MR. Antepartum and postpartum hemorrhage. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics - Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 18.

Houry DE, Salhi BA. Acute complications of pregnancy. In: Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 176.

Cunningham FG, Leveno KJ, Bloom SL, et al. Pregnancy hypertension. In: Cunnigham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 23rd ed. New York, NY: McGraw-Hill; 2010:chap 34.


Review Date: 9/12/2011
Reviewed By: Linda Vorvick, MD, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; and Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Redmond, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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