The placenta attaches to the wall of the uterus (womb) and supplies the baby with food and oxygen through the umbilical cord.
Placenta previa is a condition in which the placenta lies very low in the uterus and covers all or part of the cervix. The cervix is the opening to the uterus that sits at the top of the vagina.
Placenta previa happens in about 1 in 200 pregnancies. If you have placenta previa early in pregnancy, it usually isn’t a problem. However, it can cause serious bleeding and other complications later in pregnancy.
Normally, the placenta grows into the upper part of the uterus wall, away from the cervix. It stays there until your baby is born. During the last stage of labor, the placenta separates from the wall, and your contractions help push it into the vagina (birth canal). This is also called the afterbirth.
During labor, your baby passes through the cervix into the birth canal. If you have placenta previa, when the cervix begins to efface (thin out) and dilate (open up) for labor, blood vessels connecting the placenta to the uterus may tear. This can cause severe bleeding during labor and birth, putting you and your baby in danger.
What are the symptoms of placenta previa?
The most common symptom of placenta previa is painless bleeding from the vagina during the second half of pregnancy. Call your health care provider right away if you have vaginal bleeding anytime during your pregnancy. If the bleeding is severe, go to the hospital.
Not all women with placenta previa have vaginal bleeding. In fact, about one-third of women with placenta previa don’t have this symptom.
How is placenta previa diagnosed?
An ultrasound usually can find placenta previa and pinpoint the placenta’s location. In some cases, your provider may use a transvaginal ultrasound instead.
Even if you don’t have vaginal bleeding, a routine, second trimester ultrasound may show that you have placenta previa. Don’t be too worried if this happens. Placenta previa found in the second trimester fixes itself in most cases.
How is placenta previa treated?
Treatment depends on how far along you are in your pregnancy, the seriousness of your bleeding and the health of you and your baby. The goal is to keep you pregnant as long as possible. Providers recommend cesarean birth (c-section) for nearly all women with placenta previa to prevent severe bleeding.
If you are bleeding as a result of placenta previa, you need to be closely monitored in the hospital. If tests show that you and your baby are doing well, your provider may give you treatment to try to keep you pregnant for as long as possible.
If you have a lot of bleeding, you may be treated with blood transfusions. A blood transfusion is having new blood put into your body. Your provider also may give you medicines called corticosteroids. These medicines help speed up development of your baby’s lungs and other organs.
Your provider may want you to stay in the hospital until you give birth. If the bleeding stops, you may be able to go home. If you have severe bleeding due to placenta previa at about 34 to 36 weeks of pregnancy, your provider may recommend an immediate c-section.
At 36 to 37 weeks, your provider may suggest an amniocentesis to test the amniotic fluid around your baby to see if her lungs are fully developed. If they are, your provider may recommend an immediate c-section to avoid risks of future bleeding.
At any stage of pregnancy, a c-section may be necessary if you have dangerously heavy bleeding or if you and your baby are having problems.
What causes placenta previa?
We don’t know what causes placenta previa. However, you may be at higher risk for placenta previa if:
- You smoke cigarettes.
- You use cocaine.
- You’re 35 or older.
- You’ve been pregnant before.
- You’re pregnant with twins, triplets or more.
- You’ve had surgery on your uterus, including a c-section or a D&C (dilation and curettage). A D&C is when a doctor removes tissue from the lining of a woman's uterus. Some women have a D&C after a miscarriage.
If you've had placenta previa before, what are your chances of having it again?
If you’ve had placenta previa in a past pregnancy, you have a 2 to 3 in 100 (2 to 3 percent) chance of having it again.
How can you reduce your risk for placenta previa?
We don’t know how to prevent placenta previa. But you may be able to reduce your risk by not smoking and not using cocaine. You also may be able to lower your chances of having placenta previa in future pregnancies by having a c-section only if it’s medically necessary. If your pregnancy is healthy and there are no medical reasons for you to have a c-section, it’s best to let labor begin on its own. The more c-sections you have, the greater your risk of placenta previa.
Last reviewed: January, 2012