Placenta Previa

What is placenta previa?

The placenta is an organ that forms on the inner wall of the uterus shortly after conception. Nutrients and oxygen pass from the mother to her fetus through the placenta, which also carries waste products away from the fetus.

Normally, the placenta is attached to the uterus above the cervix. In rare cases, the placenta forms low in the uterus and is partially to completely covering the cervix. When the placenta is blocking the cervix, it is called placenta previa. See illustrations of a normal placenta and placenta previa .

What are the symptoms?

Some women with placenta previa do not have any symptoms; others have sudden, painless vaginal bleeding that ranges from slight to heavy. The blood is often bright red.

What causes placenta previa?

The specific cause of placenta previa is not known. However, there are several risk factors that can increase your chances of developing placenta previa, including:¹

• Cigarette smoking, which is strongly linked to 1 of every 4 previas.¹ Smoking decreases the amount of oxygen transferred to the fetus, thereby stimulating the growth of a larger placenta, which is more likely to grow low into the uterus.
• History of medical procedures that affect the uterine lining, such as dilation and curettage (D&C) done with sharp curettage (rare) after a miscarriage (spontaneous abortion) or a medical abortion.^{2, 3}
• Previous cesarean delivery (C-section). Of women who have had a cesarean delivery in the past, as many as 4 in 100 develop placenta previa; of women who have had four or more C-sections, 10 in 100 develop placenta previa.⁴
• History of several previous pregnancies. Placenta previa occurs in 1 in 1,500 first-time pregnancies. In women who have had five or more pregnancies, this increases to about 5 in 100.⁵
• Advancing maternal age. Among women 19 and younger, only 1 in 1,500 develops placenta previa. Of women 35 and older, 1 in 100 develops placenta previa.⁶
• Cocaine or crack cocaine use during pregnancy.⁷
• History of a previous placenta previa.

If your health professional has identified a placenta previa or low-lying placenta before your 20th week of pregnancy, chances are good that it will resolve on its own. About 90% of placenta previa cases diagnosed before the 20th week resolve on their own by the end of the pregnancy.⁴ As the lower uterus grows, the position of the placenta can change in relation to the cervix so that by the end of the pregnancy, the placenta no longer blocks the cervix.

How is placenta previa diagnosed?

Placenta previa is diagnosed with ultrasound. Most previas are identified during the second trimester, with routine ultrasound, or when assessing the cause of vaginal bleeding or when bleeding begins at the onset of labor.

How is it treated?

Treatment for placenta previa depends on how much you are bleeding and whether your fetus is mature enough to survive early delivery. Providing that you and your fetus are stable, you can be closely monitored until the baby can be safely delivered.

With a bleeding previa, it is important that you avoid sexual intercourse, office vaginal exams, or putting anything else in your vagina. (You may, however, have a carefully done vaginal exam at the hospital.)

When your fetus is mature enough, or if too much bleeding is endangering you or your fetus, your baby will be delivered. Because disturbing the placenta with a vaginal delivery can cause severe bleeding, a cesarean section is always used when placenta previa is present.

What are the potential complications of placenta previa?

Placenta previa can cause complications for both mother and fetus, including:

• Early separation of the placenta from the uterine wall (placenta abruptio).
• Severe maternal bleeding (hemorrhage) before or during delivery, which can be life-threatening for both a mother and her fetus. When the placenta has abnormally attached or grown into the uterine wall (placenta accreta, placenta increta, or placenta percreta), bleeding can be severe enough to require a hysterectomy.⁵
• Premature, or preterm, delivery (before the 37th week of pregnancy), which typically poses the greatest risk to the fetus.
• Birth defects. Birth defects occur 2.5 times more often in pregnancies affected by placenta previa than in unaffected pregnancies. The cause is currently unknown.⁶ It may just be that placenta previa is slightly more common among older women, as are babies with birth defects.

Frequently Asked Questions

Symptoms of placenta previa include one or both of the following:

• Sudden, painless vaginal bleeding that ranges from slight to heavy. The blood is often bright red. Bleeding can occur as early as the 20th week of pregnancy but is most common during the third trimester.
• Symptoms of preterm labor. One in 5 women with signs of placenta previa also has uterine contractions.⁴

Bleeding from placenta previa may taper off and even stop for a while. However, it nearly always starts again days or weeks later.

Some women with placenta previa do not have any symptoms. In this case, placenta previa may only be diagnosed by an ultrasound done for other reasons.

An ultrasound test is used to diagnose a low-lying placenta or placenta previa, in which the placenta partially or fully covers the cervix. However, ultrasound does not always provide a clear picture of the placenta's location.

Unless an immediate cesarean delivery is planned, a pelvic (vaginal) examination is not done because of the risk of further injuring the placenta, causing heavier bleeding.

Electronic fetal heart monitoring is used to check the fetus's condition.

When an early delivery is needed, an amniocentesis may be done. It is used to find out whether the fetus's lungs are ready to breathe well after birth. For an amniocentesis, a needle is inserted into the mother's belly to take a small sample of amniotic fluid from inside the uterus. This fluid is made by the fetus's lungs. A lab test of the fluid can test for signs that the lungs are well-developed.

If you have placenta previa, your treatment will depend upon:

• How much you are bleeding (which influences whether you are monitored as an outpatient or in the hospital), whether you need a blood transfusion, and when delivery is necessary.
• Your overall physical condition, such as whether you've lost blood and are anemic.
• Your fetus's overall maturity and physical condition. Whenever possible, delivery is delayed until fetal lungs are mature.
• How much of your cervix is covered by the placenta. Because a vaginal delivery is likely to cause heavy placental bleeding, a cesarean is used for placenta previa deliveries.

If you have placenta previa and are not bleeding, it is important to follow certain precautions:

• Avoid all strenuous activities, such as running or lifting more than approximately 20 lb (9.1 kg).
• See a doctor immediately if you have any bleeding. Be sure that he or she knows you have placenta previa.
• Have a phone nearby at all times.
• Advise all health professionals who examine you that you must not have pelvic examinations.
• Refrain from sexual intercourse after 28 weeks of pregnancy; before 28 weeks, ask your health professional about any possible risks.
• Avoid inserting anything, such as tampons or vaginal douches, into the vagina.
• Be close to a hospital that can provide emergency care for both you and a sick or premature infant.

If you have placenta previa and begin to bleed, you may be hospitalized. If your fetus is mature, you will have a cesarean delivery. If your bleeding lessens or stops, delivery can most likely be delayed. This watching and waiting approach is called expectant management. The course of expectant management is based on your and your fetus's condition.

• If your fetus is 24 to 34 weeks' gestation, you may be given corticosteroids to improve fetal lung development and prepare for an early birth. You may have an amniocentesis to see how developed your fetus's lungs are. You may also be given iron supplements to treat or prevent anemia and a high-fiber diet with stool softeners to ease any straining during a bowel movement. If you have Rh-negative blood, you will be given Rh immune globulin in case your fetus has Rh-positive blood. Should you be exposed to your fetus's Rh-positive blood without Rh immune globulin, your immune system will develop antibodies that are dangerous to an Rh-positive fetus (Rh sensitization). For more information, see the topic Rh Sensitization During Pregnancy.
• If your bleeding does not stop, expect to remain hospitalized and closely monitored until your fetus is mature enough to deliver. Moderate blood loss can be replaced with a blood transfusion to prolong your pregnancy until your fetus is mature enough to deliver.⁸
• If you have labor contractions, you may be given tocolytic medication to slow or stop the contractions. However, the benefit of tocolytic medications in stopping labor is uncertain. For more information, see the topic Preterm Labor.
• Should bleeding become severe and uncontrollable, an immediate cesarean delivery, possibly with a blood transfusion, is the only treatment available for stopping it. About 1 in 10 of women with placenta previa requires a hysterectomy to stop uncontrollable bleeding.⁹

Delivery

Delivery involving placenta previa is done by cesarean section.

Nearly half of placenta previa deliveries are preterm (before the 37th week of pregnancy).¹⁰ Infant problems following placenta previa are usually related to prematurity. If your infant is premature, he or she may need care in a neonatal intensive care unit, or NICU. Care in the NICU can last days or weeks, depending on the extent of a baby's problems and the amount of care needed. For more information, see the topic Premature Infant.

Treatment for placenta previa can be done by:

• An obstetrician.
• A perinatologist.

Treatment for a premature infant can be provided by a neonatologist.

If you are pregnant, be alert for any vaginal bleeding. Sudden, painless vaginal bleeding may be the only symptom of placenta previa, a placenta that partially or fully covers the cervix.

Call your health professional or go to the closest emergency room immediately if you have:

• Moderate to severe vaginal bleeding during the first trimester.
  • Severe vaginal bleeding means soaking more than one pad in 1 hour (you should not be using tampons).
  • Moderate vaginal bleeding means soaking more than eight pads in 24 hours.
• Any vaginal bleeding in the second or third trimesters.

Call your health professional today if you have mild vaginal bleeding (soaking fewer than eight pads in 24 hours) during the first trimester of pregnancy.

If you have had placenta previa

You may have questions about a future pregnancy once you have experienced placenta previa. Based on the nature of your condition, your doctor will be able to answer your questions and address your concerns.

In very rare cases, placenta previa causes a stillbirth or newborn death. Should you experience such a loss, allow yourself time to grieve. Expect that your partner, children, and other family members may also be deeply affected. Consider meeting with a support group, reading about the experiences of other women, and talking to friends, a counselor, or a member of the clergy to help you and your family cope with your loss. For more information, see the topic Grief and Grieving.

Organizations

• Cesarean Section
• Grief and Grieving
• Hysterectomy
• Pregnancy
• Pregnancy-Related Problems
• Premature Infant
• Preterm Labor
• Rh Sensitization During Pregnancy

Citations

1. Faiz AS, Ananth CV (2003). Etiology and risk factors for placenta previa: An overview and meta-analysis of observational studies. Journal of Maternal-Fetal and Neonatal Medicine, 13: 175–190.

2. Ananth CV, et al. (1997). The association of placenta previa with history of cesarean delivery and abortion: A meta-analysis. American Journal of Obstetrics and Gynecology, 177(5): 1071–1078.

3. Johnson LG, et al. (2003). The relationship of placenta previa and history of induced abortion. International Journal of Gynaecology and Obstetrics, 81(2): 191–198.

4. Baron F, Hill WC (1998). Placenta previa, placenta abruptio. Clinical Obstetrics and Gynecology, 41(3): 527–532.

5. Kay HH (2003). Placenta previa and abruption. In JR Scott et al., eds., Danforth's Obstetrics and Gynecology, 9th ed., pp. 365–379. Philadelphia: Lippincott Williams and Wilkins.

6. Cunningham FG, et al. (2005). Placenta previa section of Obstetrical hemorrhage. In FG Cunningham et al., eds., Williams Obstetrics, 22nd ed., pp. 819–823. New York: McGraw-Hill.

7. Macones GA, et al. (1997). The association between maternal cocaine use and placenta previa. American Journal of Obstetrics and Gynecology, 177(5): 1097–1100.

8. Benedetti TJ (2002). Placenta previa section of Obstetric hemorrhage. In SG Gabbe et al., eds., Obstetrics: Normal and Problem Pregnancies, 4th ed., pp. 516–520. New York: Churchill Livingstone.

9. Frederiksen MC, et al. (1999). Placenta previa: A 22-year analysis. American Journal of Obstetrics and Gynecology, 180: 1432–1437.

10. Crane JMG, et al. (1999). Neonatal outcomes with placenta previa. Obstetrics and Gynecology, 93(4): 541–544.

Author:	Kathe Gallagher, MSW	Last Updated March 15, 2006
Medical Review:	Joy Melnikow, MD, MPH - Family Medicine William Gilbert, MD - Perinatology
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