What Is Placenta Previa?

There are three types of placenta previa.

Wolters Kluwer Health, Inc.- Lippincott Williams & Wilkins.

What Is Placenta Previa?

Placenta previa is a pregnancy complication in which the placenta (the organ that grows in the uterus to provide oxygen and nutrients to the baby) attaches low within the uterus, covering all or part of the cervix. Normally, the placenta attaches to the upper part of the uterus, away from the cervix, allowing 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 by moving 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).??

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 pregnant women with placenta previa experience this symptom—about one-third do not have any bleeding at all.?? Some women may also have occasional contractions. Otherwise, this condition does not have other tell-tale signs.

Be sure to alert your medical 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 during ultrasound examinations. If a woman is experiencing 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.??

Some women may receive a diagnosis of placenta previa when they begin experiencing symptoms like bleeding or premature uterine contractions, which may lead a doctor to evaluate the placental position. This examination is also done by ultrasound.??

Causes and Risk Factors

The cause of placenta previa is unknown. It may just be a random anomaly, as the placement of the placenta in the uterus varies from woman to woman (and pregnancy to pregnancy).

It is estimated that anywhere from 1% to 15% (or more) of women may have placenta previa at some point in their pregnancy.?? However, it impacts only about 1 in 200 women in 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 women who have had a prior pregnancy with placenta previa, the rate of recurrence in subsequent pregnancies is estimated to be between 2% and 3%.??

Types

The types of placenta previa are defined according to how much of the cervix is covered up by the placenta. Types of placenta previa include the following:

  • 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)

As noted above, the position of the placenta often moves during pregnancy. So, while you may be diagnosed with one type, this diagnosis will likely change as the pregnancy progresses and the placenta migrates upwards with the growing uterus and fetus. In fact, 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.??

Potential Complications

True placenta previa at full term is a serious pregnancy complication for both the mother 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.?? Below, we look at possible complications placenta previa may cause for the baby and mother.

Impact for the Baby

Some potential complications for the baby include:??

  • Preterm birth (placenta previa causes approximately 5% of preterm births, and most pregnancies with placenta previa in later pregnancy will be delivered early)??
  • Health problems for the baby (often due to preterm birth), requiring a NICU admission
  • Intrauterine growth restriction (IUGR) due to poor placental blood supply
  • Increased risk of perinatal or neonatal death (stillbirth or babies who die within one week to one month of life)

Complications for Mother

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

Other potential risks for a mother with placenta previa include:??

  • Increased risk of placenta accreta (this is when the placenta attaches directly to the uterine muscle)
  • Increased risk of placenta previa in subsequent pregnancies??
  • Need for a cesarean delivery (this is needed unless the placenta moves far enough away from the cervical opening before delivery)
  • Preterm labor and premature rupture of membranes

Treatment

There is no cure for placenta previa. 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 using 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 mother 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.

A few more things you can do to stay healthy include the following:

  • 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.
  • Keep an eye on your symptoms.
  • Prepare (mentally and practically) for having a c-section.

A Word From Verywell

Placenta previa can be very stressful for all involved. Luckily, most often, the condition will resolve without necessitating a preterm delivery and/or cesarean section. Even if your placenta stays put, with appropriate prenatal care, you are very likely to have a safe delivery.

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