Pregnancy: Placenta Previa in Twentieth Week

In my wife's twentieth week of pregnancy she had an ultrasound and the doctor detected partial placenta previa. He told us that at this time it is pretty common for that condidtion to exist. He then said that he would do another ultrasound at 30 weeks. Is this really common and what are the odds that the placenta will have moved far enough up to not become a problem? What will happen if it doesn't move?


Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

According to Williams Obstetrics, placenta previa diagnosed at less than 20 weeks gestation has a subsequent chance of placenta previa and/or hemorrhage at delivery of 2.3 percent; diagnosis at 20 to 25 weeks carries a possibility of 3.2 percent; 25 to 30 weeks of 5.2 percent; and 30 to 35 weeks of 23.9 percent. The actual incidence at the time of delivery is small, about 0.3 to 0.5 percent.

The authors of this text believe that, due to the low frequency with which placenta previa persists when it has been identified by ultrasound before 30 weeks, sonograms need not be frequently repeated simply to follow placental migration upward. (As long as there are no other abnormalities.)

A repeat ultrasound at 30 weeks is very appropriate. If it is still a partial previa at that time, more ultrasounds will be done to follow migration. If this does occur, your wife will be given instructions to watch for any spotting to notify her doctor if that should happen. Hemorrhage that may affect the baby's survival is not likely to happen with the first episode of bleeding. If bleeding persists, no one should do vaginal exams on her unless they are ready to perform an immediate cesarean.

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