When the placenta, which conducts blood from the mother's body to the developing fetus, is located so low in the uterus that it lies across the cervix (the opening of the womb), the condition is called placenta previa. The placenta may cover part or all of the cervix, blocking the baby from coming out. In about one out of 200 births, placenta previa persists until birth.

No one knows what causes the placenta to grow across the cervix, but placenta previa is associated with certain risk factors.

The likelihood of placenta previa goes up with the number of deliveries a woman has had. So if you have been pregnant before, and especially if this is your third or fourth child, your risk is considerably higher. Placenta previa is also more common in women who are carrying multiples. There's additional risk if you have had placenta previa in an earlier pregnancy, or if you've had fibroid tumors or previous uterine surgery such as a c-section.Mothers-to-be who are over age 35, cigarette smokers, or cocaine users are also more likely to develop the condition. Just remember, however, that even if you have these risk factors, the chance of having placenta previa is still very low -- about a half of one percent.

In many cases, there are no symptoms. But painless bleeding that suddenly begins during the second half of pregnancy is the most common sign of placenta previa. If this happens, your doctor will probably recommend that you go to the hospital immediately for an evaluation and ultrasound exam.

Even if you don't experience any bleeding, your practitioner can determine the position of the placenta as part of a routine ultrasound at about 18 to 20 weeks. If the images show the placenta to be near the cervix, there is no immediate cause for alarm, as the placenta will likely move up and out of the way as your uterus grows. If placenta previa is not detected at all during this period, you can stop worrying about it. It's unusual for placenta previa to occur after the 18th week.

If the ultrasound shows that your placenta is covering your cervix, it can be tracked closely with follow-up sonograms and treated accordingly.

There is no treatment that can change the location of your placenta, but it's possible your doctor may give you medications and order bed rest to prevent premature labor. Your treatment will depend on how early in your pregnancy the problem is discovered, whether there is significant bleeding, and whether it appears to be harming the baby. If placenta previa is diagnosed after the 20th week and there is no serious bleeding, your practitioner may restrict your activity somewhat or put you on bed rest. Talk to your doctor about what you can do to reduce the risks.

If there is significant bleeding, you will need to be hospitalized so your condition can be stabilized. You may also receive steroid injections to help the baby's lungs develop faster in case she needs to be delivered early. In almost all cases of placenta previa, the baby needs to be delivered via c-section to prevent hemorrhage. If you experience bleeding that doesn't stop or if you go into preterm labor, your baby may need to be delivered by c-section.

-- Melanie Haiken, MA, is the former health editor of Parenting magazine. She has also reported on health and business.

References

First published September 6, 2005
Last updated March 27, 2008
Copyright © 2005 Consumer Health Interactive

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