The placenta nourishes and protects your baby throughout pregnancy, filtering out what she doesn’t need and delivering the oxygen and nutrients she does.
Most of the time, it attaches to the upper part of the uterus. But if it settles in the lower part of the uterus, you might be diagnosed with placenta previa, or your doctor might say you have a low-lying placenta.
What is placenta previa?
Placenta previa is a relatively rare pregnancy complication in which the placenta implants low in the uterus and covers part or all of the cervix.
Currently, placenta previa is defined as any instance where the placenta covers part or all of the cervix.
Previous categories of the condition, including marginal previa (when the placenta is within 2 centimeters of the cervix but doesn't physically cover it), partial previa (when the placenta covers part of the cervical opening) and complete previa (when the placenta covers the entire cervical opening) are no longer used.
Instead, in all cases of previa, the placenta physically blocks the opening to the birth canal (the vagina) in some way. That can cause bleeding during pregnancy and labor, and may affect how your baby comes into the world when it's time to deliver.
What’s a low-lying placenta and does it mean I'll have placenta previa?
A placenta that is close to but not covering the cervical opening (usually within 2 centimeters) is called a low-lying placenta. During the second trimester of pregnancy, often during your 20-week anatomy scan, your doctor may tell you that you have this condition.
In roughly 9 out of 10 cases, a low-lying placenta resolves on its own and won’t be considered placenta previa by the time you give birth. As the uterus grows in the third trimester, the placenta will “migrate” on its own, moving up and away from the cervix.
More About the Placenta and Umbilical Cord
If your doctor sees that you have a low-lying placenta in the first or second trimester, he or she will recommend a follow-up ultrasound between weeks 28 and 32 of pregnancy to check the location of the placenta.
How common is placenta previa?
Placenta previa occurs in about 1 out of every 200 deliveries.
If you’re told you have a low-lying placenta or placenta previa before 28 weeks, try not to worry. Many women are diagnosed with placenta previa in the second trimester, usually during a routine ultrasound.
The majority of cases of placenta previa that are diagnosed in the first two trimesters resolve by the third trimester, meaning that the placenta moves up and away from the cervix before delivery.
In fact, your practitioner may not even mention a possible previa to you until your third trimester, since the odds are that it won’t persist until then.
Who is most at risk of placenta previa?
Placenta previa risk factors include:
- Age. Placenta previa is more likely to occur in women over the age of 30 than in those under the age of 20.
- Second or later pregnancy. The condition is more common in women who have had at least one other pregnancy.
- Multiples. Being pregnant with two or more babies increases your likelihood of placenta previa.
- Prior C-section or uterine surgery. Scarring on the uterus due to previous surgeries, including C-sections, uterine fibroid removal and D and C procedures, increases the risk of placenta previa.
- Smoking or drug use. Cigarette or cocaine use during pregnancy increases your chances of developing a host of complications, including placenta previa.
- Race. Some research suggests that Asian and Black women have a greater risk of placenta previa than other racial groups.
- In vitro fertilization (IVF). Assisted reproductive technology including IVF has been linked to an increased risk of placental problems, including placenta previa.
What are the symptoms of placenta previa?
Placenta previa or a low-lying placenta is usually discovered and diagnosed not on the basis of symptoms but during a routine second-trimester ultrasound.
Sometimes the condition announces itself in the third trimester and occasionally earlier with the following symptoms:
- Bleeding. Placental problems, including placenta previa, are the most common cause of heavy vaginal bleeding in the latter part of pregnancy. About 2 in 3 women with placenta previa experience some painless, bright red bleeding (not just vaginal spotting, which is often normal). However about 1 in 3 women with the condition don’t bleed at all.
- Cramping. While it’s not common to feel pain, some women with placenta previa experience cramping or contractions, though it usually happens in conjunction with bleeding.
- Breech position. Your baby is more likely to be in a breech position when you have placenta previa. That’s because in a typical pregnancy, the most comfortable third trimester position for a baby is head-down at the bottom of the uterus, where there’s the most room. But with placenta previa, the placenta occupies that space where your baby’s head would normally gravitate. That may cause her to stay in (or move to) a breech position.
How can I stop bleeding from placenta previa?
As your cervix begins to dilate and efface in preparation for birth, there may be tearing in the blood vessels that connect the placenta to the uterus in the area over the cervix. This may cause bleeding. The risk of bleeding increases if more of the placenta covers the cervix.
There’s no way to prevent placenta previa, and no surgical or medical procedure can correct the condition. However many bleeding incidents can be treated effectively before blood loss puts you or your baby at risk. Managing light bleeding usually includes avoiding activities that can cause bleeding, like exercise and sex.
Severe and uncontrolled bleeding, especially if your baby is in distress, may be cause for an immediate delivery. Head to the emergency room right away if you experience heavy bleeding.
How is placenta previa treated?
If you’re diagnosed with placenta previa, you'll want to keep a lookout for heavy bleeding as well as signs of preterm labor, which is more common with placenta previa.
Your doctor’s goal is to get you as close to your due date as possible. Once you’ve reached your third trimester, your health care provider may recommend measures to ensure a safe pregnancy and delivery, especially if you experience bleeding. These might include:
- Pelvic rest. This means abstaining from sex, discontinuing any use of tampons or vaginal douches, and foregoing pelvic exams.
- Increased fetal monitoring. Your doctor may want to keep an eye on your baby to make sure her heartbeat remains strong and her movements are consistent.
- Medications. Your doctor may provide you with medications to prevent early labor and increase the odds that your pregnancy will continue to at least 36 weeks. If prenatal testing early on in your pregnancy reveals you’re Rh negative, you may also receive shots of a special Rh-incompatibility treatment known as RhoGAM.
- Bed rest. Because prolonged inactivity can lead to complications including muscle atrophy and increased risk of blood clots, doctors usually avoid prescribing strict bed rest during pregnancy. However your doctor may recommend restricting activity, such as exercise, walking or standing for long periods of time.
- Hospital care. Your practitioner may want you to remain at a hospital until your delivery, particularly if you’ve had a bleeding incident, in order to monitor you and your baby continuously.
Can you deliver naturally with placenta previa?
It’s sometimes possible to have a vaginal delivery with placenta previa, but most women deliver via C-section to avoid potentially life-threatening bleeding.
If you have complete or partial covering of the cervix in the third trimester, you will deliver via C-section, and about 75 percent will be scheduled C-sections before labor starts. If the placenta previa resolves and your placenta doesn’t cover the cervix, you may be able to have a vaginal delivery.
If you haven’t yet reached 37 weeks of pregnancy and preterm delivery is necessary, you’ll receive steroid shots to rapidly mature your baby's lungs before a C-section is performed. If severe bleeding occurs after 36 weeks, your practitioner may recommend an immediate cesarean.
Other placenta previa complications
A placenta previa diagnosis during the third trimester means that your practitioner may not be able to stick to your birth plan. And a previa-induced bleeding incident, if you experience one, can be frightening.
While placenta previa itself isn’t dangerous for you or your baby, it can lead to serious bleeding and preterm birth. Your doctor will monitor you closely and take precautions to prevent complications.
Possible complications of placenta previa include:
- Preterm birth. Placenta previa increases the risk of your baby being born before her due date. Preterm delivery, in turn, is linked to babies having a lower birth weight and lower APGAR scores.
- Placenta accreta. Placenta previa is a risk factor for placenta accreta, which is when the placenta attaches too deeply to the uterine wall. This can cause life-threatening bleeding in the third trimester and at the time of delivery, which is why your doctor will almost always recommend a scheduled C-section before your due date. The risk is higher if you've had a previous C-section.
- Vasa previa. This very rare pregnancy complication, which happens in about 1 in 2,500 pregnancies, occurs when the fetal blood vessels from the placenta cross the opening to the vagina. It’s more common (although still rare) if you have placenta previa. Because vasa previa can lead to fatal fetal hemorrhage when the cervix begins dilating or the membranes rupture, your doctor will plan for an early cesarean delivery.
- Hemorrhage and hysterectomy. If you have placenta previa, bleeding can sometimes become uncontrolled during labor or in the hours following delivery. In rare cases, severe bleeding may require a blood transfusion and/or hysterectomy (i.e. removal of the uterus).
- Increased risk in future pregnancies. Having placenta previa during pregnancy increases the risk of having placenta previa and preterm birth in future pregnancies.
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