What Is Placenta Previa?

There are three types of placenta previa.

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Placenta previa is a pregnancy complication in which the placenta (the organ that grows in the uterus to provide oxygen and nutrients to the fetus) attaches low within the uterus, covering all or part of the cervix. The main placenta previa symptom is vaginal bleeding.

Normally, the placenta attaches to the upper part of the uterus, away from the cervix. This allows for optimal blood supply and oxygenation of the placenta—and safe exit for the baby during labor and delivery. 

Placenta previa can be problematic later on in pregnancy, as it may cause severe bleeding, leading to preterm delivery. In many cases, placenta previa will resolve on its own if the placenta moves up the uterine wall away from the cervical opening (or cervical os). However, this condition persists in 0.3% to 0.5% of pregnancies at delivery, necessitating a cesarean section (or C-section).

Placenta Previa Symptoms

The most common (and noticeable) symptom of placenta previa is painless, bright red vaginal bleeding during the second trimester. It can also occur sometimes in the third trimester. However, not all people with placenta previa experience this symptom—about one-third do not have any bleeding at all. Some may also have occasional contractions. Otherwise, this condition does not have other tell-tale signs.

Be sure to alert your healthcare provider if you experience vaginal bleeding at any time during your pregnancy. If bleeding is severe, go to the emergency room and/or call 911.

Diagnosis

Placenta previa is most often diagnosed by ultrasound. If a pregnant person is experiencing vaginal bleeding, an ultrasound may be done to check the placental position.

Also, typical prenatal care involves routine ultrasound around the 20th week of pregnancy, where doctors check for this condition. The good news is that 90% (or more) of placenta previa cases resolve on their own.

Types

Placenta previa is described according to how much of the cervix is covered up by the placenta. There are three main types of placenta previa:

  • Complete previa: The cervical opening (where the cervix opens into the uterus) is completely covered by the placenta.
  • Partial previa: Some of the cervical opening is covered by the placenta.
  • Marginal previa: The placenta extends to the edge of the cervix (close by but not covering it).

Since the placenta often moves during pregnancy, the type of placenta previa you have (or its presence at all) can change as the pregnancy progresses. In one study of over 1,200 placenta previa cases, all but 1.6% resolved before delivery.

If you have a complete previa, the placenta is less likely to move completely off of the cervical opening than with partial or marginal previas. Additionally, the later in the pregnancy that you have this condition, the less likely it is to resolve before delivery.

Causes and Risk Factors

Doctors and scientists don't know what causes placenta previa. It may just be a random anomaly, as the placement of the placenta in the uterus varies from person to person (and pregnancy to pregnancy).

Anywhere from 1% to 15% (or more) of people may have placenta previa at some point in their pregnancy. However, it affects only about 1 in 200 people by the third trimester.

The odds of this condition occurring in your pregnancy increase if you have one or more of the following risk factors:

  • Advanced maternal age (35 or over)
  • Being pregnant with more than one baby (for example, twins or triplets)
  • Cocaine use
  • Increased parity (number of pregnancies)
  • Infertility treatment
  • Previous placenta previa
  • Previous uterine surgery, including cesarean section (regardless of incision type) or a D&C
  • Prior abortion
  • Smoking cigarettes

For people who had a prior pregnancy with placenta previa, the rate of recurrence in subsequent pregnancies is estimated to be between 2% and 3%.

Potential Complications

True placenta previa at full term is a serious pregnancy complication for both the parent and baby. Pregnancies with persistent placenta previa need to be carefully monitored, as this condition is one of the leading causes of maternal hemorrhage and death as well as of preterm birth.

Effects on the Fetus

Some potential complications for the fetus include:

  • Health problems: These babies may be born with medical conditions requiring a NICU admissions (often due to preterm birth).
  • Increased risk of death: If their gestational parent has placenta previa, babies are at risk of perinatal or neonatal death (stillbirth or dying in the first month of life).
  • Intrauterine growth restriction (IUGR): Poor placental blood supply can limit the fetus's growth, which in turn can cause health problems.
  • Preterm birth: Placenta previa causes approximately 5% of preterm births, and most pregnancies with placenta previa in later pregnancy will be delivered early.

Complications for the Parent

For pregnant people in countries with access to high-quality medical care, like the United States, placenta previa is rarely fatal. But severe bleeding may occur prior to, during, or after labor and delivery. Sometimes, a parent may require blood transfusions for life-threatening bleeding. 

Other potential risks for a pregnant person with placenta previa include an increased risk of placenta accreta (when the placenta attaches directly to the uterine wall) and increased risk of placenta previa in subsequent pregnancies.

Some people with placenta previa will need a cesarean delivery (unless the placenta moves far enough away from the cervical opening before delivery). There is also a risk of preterm labor and premature rupture of membranes.

Treatment

There is no cure for placenta previa; there is no way to make the placenta move into a better position. The only treatment is delivering the baby by c-section. If the placenta previa does not resolve on its own, you will need monitoring, particularly if you are having vaginal bleeding.

If you have persistent placenta previa (into the third trimester) and/or vaginal bleeding, it's generally recommend to take it easy. Sometimes, you'll need to go on bed rest, possibly in the hospital, until delivery.

Your doctor also may advise that you avoid sex, strenuous exercise, and tampons (which should never be used in pregnancy anyway). If bleeding or other complications persist, an early delivery will be considered to protect the lives of both parent and baby. When preterm delivery is imminent, if the gestational age is before 37 weeks, steroid shots may be given to help mature the baby's lungs.

Coping

For the most part, coping with placenta previa is about being patient and kind to yourself while you wait to find out if your placenta moves into a better position. Know that it's not your fault. Seek out support from loved ones and/or counseling or a support group, particularly if you're on bed rest and need more help.

You can also:

  • Be aware of how far you are from a hospital and aim to stay close by when possible (under 20 minutes is ideal).
  • Be ready for a preterm delivery (including having a car seat, diapers, and other baby necessities on hand).
  • Call your doctor if you notice any vaginal bleeding or contractions.
  • Prepare (mentally and practically) for having a c-section.

A Word From Verywell

Placenta previa can be very stressful for all involved. Luckily, the condition often resolves before a preterm delivery and/or cesarean section becomes necessary. Even if your placenta stays put, with appropriate prenatal care, you are very likely to have a safe delivery.

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9 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.