Placenta previa occurs in about one in 200 pregnancies. Women who've had a placenta previa in a previous pregnancy have a 4 to 8 percent chance of a recurrence. The most common symptom of placenta previa is painless uterine bleeding.
The cause of placenta previa is unknown, but like placental abruption, a condition in which the placenta separates from the uterine wall, it's more common among women who smoke, use cocaine, or are over age 35. Women are also at increased risk if they've had previous uterine surgery, including a c-section, a D&C (dilation and curettage, in which the lining of the uterus is scraped) following a miscarriage, an abortion, or if they are carrying twins (or a higher number of multiples).
Your doctor will do an ultrasound exam to diagnose placenta previa and pinpoint the placenta's location. You'll probably need to stay in the hospital until delivery. If the bleeding stops, which it usually does, your physician will continue to monitor both you and baby. If the bleeding does not stop, or if you go into labor, your doctor will probably suggest a c-section.
If you haven't yet gone into labor but your doctor thinks you may deliver before 34 weeks, she'll probably recommend treatment with corticosteroids. At 36 weeks, if you haven't delivered, she may also suggest a test called amniocentesis to see if your baby's lungs are mature. Provided they are, she will likely suggest a c-section to prevent serious uterine bleeding.
Some women learn during a routine ultrasound that they have a low-lying placenta. More than 90 percent of the time, placenta previa diagnosed in the second trimester corrects itself by term. You don't need to restrict your activities or undergo any treatment. Your doctor will probably recommend another ultrasound at about 28 weeks, though, to make sure the placenta has moved away from the cervix. In the unlikely event that it hasn't, she may recommend that you cut back on activities and rest in bed.
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