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Placenta Previa

Definition

The placenta is an organ that develops in the uterus during pregnancy. Its purpose is to nourish the baby. Oxygen and nutrients pass through the placenta to the baby. Waste products pass back out to the mother’s blood stream.

Placenta previa occurs when the placenta becomes implanted near or over the cervix. The cervix is the lower part of the uterus that opens into the vagina. With this condition, the placenta may cover part or all of the cervix. This condition is only diagnosed after 20 weeks of gestation.

Placenta Previa
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Causes

Possible causes of placenta previa include:

  • A scarred endometrium—the lining of the uterus
  • A large placenta
  • An abnormal uterus
  • Abnormal formation of the placenta

Placenta previa can cause problems in pregnancy and birth. These include:

  • Abnormal bleeding, sometimes heavy
  • Premature separation of the placenta from the uterus
  • Premature birth
  • Emergency cesarean (c-section) delivery
  • Problems with penetration of the placenta into the uterine muscle or through the entire uterine wall

Risk Factors

Factors that may increase your chance of developing placenta previa include:

  • Previous cesarean section
  • Uterine problems
  • Multiple pregnancy—two or more fetuses
  • Multiple previous full-term pregnancies
  • Increased age
  • Smoking

Symptoms

Placenta previa symptoms vary depending on how much of the cervical opening is covered. The main symptom is painless bleeding from the vagina. This bleeding can range from light to very heavy. It usually occurs suddenly during late pregnancy. Spotting that occurs early in pregnancy may point to placenta previa.

Anything that disrupts the placenta, such as sexual intercourse, or digital exam of the vagina and cervix, may cause bleeding.

Complications

Complications of placenta previa include:

  • Major bleeding
  • Increased risk of infection
  • Increased likelihood of a blood transfusion
  • Premature birth, which occurs when an infant is less than 37 weeks of gestation
  • Fetal blood loss during labor
  • Shock
  • Maternal or fetal death

Diagnosis

The doctor will ask about your symptoms and medical history. A physical exam will be done. A pelvic exam will not be done if placenta previa is a possibility. A pelvic exam may cause bleeding. Instead, an ultrasound will be done through the vagina or abdomen to view the placenta in the uterus. If placenta previa is detected early in pregnancy, with or without bleeding, another ultrasound will be done during the third trimester to be sure it has resolved.

If you had cesarean section in the past, and the ultrasound indicates a potential problem with the placenta, your doctor may recommend an MRI scan .

Treatment

Treatment depends on several factors, including the amount of bleeding and the gestational age of the fetus. Recommendations for treatment include:

  • Pelvic rest—avoid sexual intercourse and tampon use if placenta previa continues into third trimester
  • Hospitalization for major placenta previa at or beyond 34 weeks of gestation
  • Medications to prolong your pregnancy and help with growth of fetal lungs with symptomatic placenta previa or bleeding at 24-34 weeks

How you will delivery your baby depends on your ultrasound results at 36 weeks of gestation. There is a possibility that the placenta previa will go away on its own. A cesarean section may be necessary if the placenta covers the opening of the cervix, there is heavy bleeding at delivery, or other serious complications arise that affect the health of the mother and baby.

Prevention

There are no current guidelines to prevent placenta previa.

Revision Information

  • American Congress of Obstetricians and Gynecologists

    http://www.acog.org

  • FamilyDoctor.org - American Academy of Family Physicians

    http://familydoctor.org

  • Health Canada

    http://www.hc-sc.gc.ca

  • Women's Health Matters

    http://www.womenshealthmatters.ca

  • Placenta previa. American Pregnancy Association website. Available at: http://americanpregnancy.org/pregnancycomplications/placentaprevia.html. Updated May 2007. Accessed August 6, 2013.

  • Placenta previa. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated October 15, 2012. Accessed August 6, 2013.

  • Pregnancy complications. US Office on Women's Health website. Available at: http://www.womenshealth.gov/pregnancy/you-are-pregnant/pregnancy-complications.html. Updated September 27, 2010. Accessed August 6, 2013.

  • 5/12/2014 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Podrasky AE, Javitt MC, et al. American College of Radiology (ACR) Appropriateness Criteria for second and third trimester bleeding. Available at: http://www.acr.org/~/media/ACR/Documents/AppCriteria/Diagnostic/SecondAndThirdTrimesterBleeding.pdf. Updated 2013. Accessed May 12, 2014.