Placenta previa is a problem 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 shaped uterus
Many previous pregnancies
Multiple pregnancy (twins, triplets, etc.)
Scarring on the lining of the uterus, due to history of surgery, c-section, previous pregnancy, or abortion
Women who smoke or have their children at an older age may also have an increased risk.
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.
Signs and tests
Your health care provider can diagnose this condition with a pregnancy ultrasound.
Your health care provider 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.
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 both the mother and the baby.
If the placenta is near or covering a part of the cervix, your doctor may recommend:
Reducing your activities
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.
Other treatments you may receive:
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
An emergency c-section may be done if the bleeding is heavy and cannot be controlled.
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.
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.
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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.
A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously 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 (9/12/2011).