Placenta previa happens when the placenta lies low in the uterus and covers all or part of the opening to the vagina.
If you develop the condition early in your pregnancy, it usually isn’t a problem since the placenta grows upward with the uterus during pregnancy.
If you develop the condition later in pregnancy and the birth canal is blocked it can cause serious bleeding and may prevent vaginal delivery.
Talk with your providers about ways to deal with placenta previa, which could include having a planned c-section (caesarean birth).
The placenta attaches to the wall of the womb (uterus) 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 opening to the cervical opening 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 because it may resolve as the pregnancy grows. However, if it persists 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, after the baby is born the placenta separates from the wall, and your contractions help push it into the birth canal (vagina). 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 thin out (efface) and open up (dilate), 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.
If a placenta previa is identified by ultrasound and appears to block the cervix, no vaginal exams are performed and an elective c-section is planned.
What causes placenta previa?
No one knows what causes placenta previa. However, you may be at higher risk for placenta previa if you:
- Have had a c-section in the past.
- Have had in vitro fertilization for infertility.
- Smoke cigarettes.
- Use cocaine.
- Are 35 or older.
- Have been pregnant before.
- Are pregnant with twins, triplets or more.
- Have had placenta previa in an earlier pregnancy.
- Have had surgery on your internal reproductive organs, such as myomectomy or tissue removal from the lining of your uterus (this is also called dilation and curettage or D&C). Some people have a D&C after 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.
What are the symptoms of placenta previa?
Most of the time, placenta previa has no symptoms; it is often found during a routine ultrasound test.
For those who do have symptoms, the most common is painless bleeding from the vagina during the second half of pregnancy. You also may have contractions. 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 everyone who has placenta previa has vaginal bleeding. In fact, about one-third of people with placenta previa don’t have this symptom.
How is placenta previa diagnosed?
A prenatal test that uses sound waves to show a picture of your baby in the womb (ultrasound) usually can find placenta previa and determine the placenta’s location. In some cases, your provider may do an ultrasound through the birth canal (transvaginal ultrasound) or a translabial ultrasound instead. In places where it’s available, three-dimensional ultrasound may be used.
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 requires repeat follow-up ultrasounds to assure that the cervix is no longer blocked. If the placenta is no longer covering the cervical opening, you can usually have a vaginal delivery.
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. Your provider may recommend no vaginal exams or sex to prevent damage to the placenta and bleeding. Providers recommend c-section for nearly everyone with placenta previa to prevent severe bleeding.
If you are early in your pregnancy and have no symptoms, your provider will probably recommend no treatment, but will schedule follow-up ultrasounds to make sure everything is normal.
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 by having new blood put into your body (blood transfusions). Your provider also may give you medicines called corticosteroids to help speed up development of your baby’s lungs and other organs in case a preterm delivery is needed.
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 the lungs are fully developed. If they are, your provider may recommend an immediate c-section to avoid risks of future bleeding. Nowadays, providers may use corticosteroids to help the baby lung development while you are pregnant and to help avoid an immediate c-section.
At any stage of pregnancy, an emergency c-section may be necessary if you have dangerously heavy bleeding or if you and your baby are having problems.
Is there anything you should avoid if you have placenta previa?
If you have placenta previa that doesn’t require immediate treatment right away, your provider may recommend that you avoid doing the following:
- Having sex that leads to orgasm
- Vaginal penetration or vaginal examinations
- Moderate and strenuous exercise
- Lifting more than 20 pounds
- Standing for more than four hours
All of these activities could lead to contractions that could lead to bleeding.
How can you reduce your risk for complications if you have placenta previa?
Have an ultrasound in the second trimester to identify location of the placenta. You may need follow up ultrasounds to help plan for a safe birth and delivery.
Follow your providers precaution instructions to prevent bleeding or complications. Contact your provider and go to the hospital if you have bleeding at any time during your pregnancy.
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.
Last reviewed: January, 2022