What is placenta previa?
Placenta previa is a pregnancy problem in which the placenta blocks the cervix. The placenta is a round, flat organ that forms on the inside wall of the uterus soon after conception. During pregnancy, it gives the baby food and oxygen from the mother.
In a normal pregnancy, the placenta is attached high up in the uterus, away from the cervix. In placenta previa, the placenta forms low in the uterus and covers all or part of the cervix.
If placenta previa is present during labor and delivery, it can cause problems for both mother and baby.
- The mother may lose a lot of blood, which can be dangerous for both her and her baby.
- The placenta may separate too early from the wall of the uterus. This is called placenta abruptio, and it can cause serious bleeding, too.
- The baby may be born too early (premature), at a low birth weight, or with a birth defect.
What causes placenta previa?
Doctors aren't sure what causes this problem. But some things make you more likely to have it. These are called risk factors.
You can't control most risk factors for placenta previa. For example, you're more likely to have it if you:
- Have had a surgery that affected your uterus, such as a D&C or surgery to remove uterine fibroids (myomectomy).
- Have had a previous C-section (cesarean delivery).
- Have had five or more pregnancies.
- Are age 35 or older.
- Have had placenta previa before.
Risk factors you can control include:
- Smoking during pregnancy.
- Using cocaine during pregnancy.
What are the symptoms?
Some women with placenta previa don't have any symptoms. But others may have warning signs such as:
- Sudden, painless vaginal bleeding. The blood is often bright red, and the bleeding can range from light to heavy.
- Symptoms of preterm labor. These include regular contractions and aches or pains in your lower back or belly.
Call your doctor if you have:
- Medium to heavy vaginal bleeding during the first trimester.
- Any vaginal bleeding in the second or third trimester.
How is placenta previa diagnosed?
Most cases of placenta previa are found during the second trimester when a woman has a routine ultrasound. Or it may be found when a pregnant woman has vaginal bleeding and gets an ultrasound to find out what is causing it. Some women don't find out that they have placenta previa until they have bleeding at the start of labor.
A pelvic exam will not be done unless you need a C-section right away. A pelvic exam could injure the placenta and cause heavier bleeding.
How is it treated?
The kind of treatment you will have depends on:
- Whether or how much you are bleeding.
- How the problem is affecting your health and your baby's health.
- How close you are to your due date.
If your doctor finds out before your 20th week of pregnancy that your placenta is low in your uterus, chances are very good that it will get better on its own. The position of the placenta can change as the uterus grows. So by the end of the pregnancy, the placenta may no longer block the cervix.
If you aren't bleeding, you may not need to be in the hospital. But you will need to be very careful.
- Avoid all strenuous activity, such as running or lifting.
- Don't have sex, and don't put anything in your vagina.
- Call your doctor and go to the emergency room right away if you have any vaginal bleeding.
If you are bleeding, you may have to stay in the hospital. If you are close to your due date, your baby will be delivered. Doctors always do a C-section when there is a placenta previa at the time of delivery. A vaginal delivery could disturb the placenta and cause severe bleeding.
If your bleeding can be slowed or stopped, your doctor may delay delivery and monitor you and your baby closely. The doctor may do fetal heart monitoring to check your baby's condition.
You may be given:
- A blood transfusion if you've lost a lot of blood.
- Steroid medicines if you aren't close to your due date. These medicines help get your baby ready for birth by speeding up lung development.
- Tocolytic medicine to slow or stop contractions if you are in preterm labor.
If your newborn is premature, your baby may be treated in a neonatal intensive care unit, or NICU. Premature babies need to stay in the hospital until they can eat, breathe, and stay warm on their own.
Other Works Consulted
- Hull AD, Resnik R (2014). Placenta previa, placenta accreta, abruptio placentae, and vasa previa. In RK Creasy et al., eds., Creasy and Resnik's Maternal-Fetal Medicine, 7th ed., pp. 732–742. Philadelphia: Saunders.
- Williams DE, Pridjian G (2011). Obstetrics. In RE Rakel, DP Rakel, eds., Textbook of Family Medicine, 8th ed., pp. 359–401. Philadelphia: Saunders.
Current as of: February 11, 2020
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
Elizabeth T. Russo MD - Internal Medicine