Placenta previa is a condition that occurs during pregnancy when the placenta implants itself in the lower part of the uterus, obstructing the cervical opening to the vagina (fig. 1).
During pregnancy, your placenta repositions itself as your uterus stretches and grows. By your third trimester, the placenta should be near the top of your uterus, leaving the cervical opening clear for the delivery. Sometimes, though, the placenta remains in the lower portion of the uterus, partly or completely covering the cervical opening. This condition, called placenta previa, makes a vaginal delivery virtually impossible and, in some cases, causes severe bleeding or hemorrhage.
There are three types of placenta previa:
- Marginal: The placenta is located near the margin of the cervix but does not block it.
- Partial: The placenta covers part of the cervical opening.
- Complete: The placenta completely covers the cervical opening.
Placenta previa occurs in one out of 200 pregnancies. It is more common in women who have uterine fibroids, an abnormally developed uterus, or scarring of the uterine wall caused by previous pregnancies, cesareans, uterine surgery, or abortions. Women who smoke or have their children at an older age may also have an increased risk.
How Do I Know I Have It?
The main symptom of placenta previa is painless vaginal bleeding that often occurs near the end of the second trimester or beginning of the third trimester. There is no abdominal pain or tenderness associated with the bleeding. The flow may be light or heavy, and the color may be bright red. The bleeding may stop on its own but can start again days or weeks later.
Your health-care provider will diagnose your symptoms and detect the location of your placenta with an ultrasound exam.
About 7% to 30% of women with placenta previa do not experience vaginal bleeding as a symptom before delivery. In these cases, diagnosis may result from a routine ultrasound exam. Sometimes the condition remains undiscovered until delivery.
How Can I Treat It?
If the placenta is near the cervix or is covering a portion of it, you may be placed on a modified schedule with bed rest. If there is bleeding, however, you will most likely be admitted to a hospital for careful monitoring. Sometimes blood transfusions are administered to replace maternal blood loss and prolong the pregnancy to at least 36 weeks. Once you reach a healthy delivery date, your health-care provider will most likely deliver your baby by cesarean section. An emergency cesarean may be induced earlier if the placenta actually covers the cervix and the bleeding is heavy or life threatening. Even if your baby is delivered prematurely, he is better off in the hands of skilled medical professionals than attached to a placenta that is no longer able to support him.
Vaginal delivery may be attempted if placenta previa is not discovered until labor has begun, bleeding is light, and the placenta is not blocking the cervix. Usually, though, three out of four women who have placenta previa deliver their babies by cesarean section.
Since in most cases placenta previa can be detected accurately before the fetus is in significant danger, it no longer poses as much of a threat to babies and mothers as it once did. Women with placenta previa have successful deliveries 99% of the time.
How Can I Prevent It?
While placenta previa cannot actually be prevented, it's best to be aware of conditions that may cause it. If you have a history of uterine fibroids, cesarean section, an abnormally developed uterus, or scarring of the uterine wall caused by several pregnancies, abortions, or uterine surgery, make this known to your health-care provider as soon as you know you're pregnant.
Frequently Asked Questions
Q: I am two months pregnant and have a low-lying placenta. Should I be worried that I have placenta previa?
A: In early pregnancy, a low-lying placenta is very common. But as your pregnancy progresses, the enlarging uterus should "pull" the placenta toward the top of your uterus. Your health-care provider will monitor the progression of your placenta throughout your pregnancy. If your placenta is still lying low in your third trimester, your doctor may suspect placenta previa.
Q: I've had placenta previa before. What are my chances of getting it again during my next pregnancy?
A: The incidence of placenta previa increases with each pregnancy. Most likely your next baby will be delivered by cesarean section to avoid any unnecessary risk, such as hemorrhaging.
Q: What's the difference between placenta previa and placenta abruptio?
A: With placenta previa, the placenta is located over or near the cervix, in the lower part of the uterus. The placenta usually blocks the cervical opening to the vagina. With placenta abruptio, the placenta partially or completely detaches itself from the uterine wall prematurely, before delivery of the baby takes place.
Review Date: June 29, 2001
Reviewed By: Peter Chen, M.D., Obstetrics and Gynecology, University of
Pennsylvania School of Medicine. Review provided by VeriMed Healthcare
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