Christian Doulas

Placenta Previa

Placenta Previa is a serious condition in which the placenta attaches at the base of the uterus, blocking the cervical opening. In the picture to the left, you can see how there are different types of placement that are called "previa": a low-lying placenta, which doesn't interfere with the cervix, a partial placenta previa, which is more serious, and a complete previa, which fully covers the cervical opening and requires a surgical delivery. If you are diagnosed with previa, you may be asked to go on bedrest in order to avoid dangerous bleeding. You almost certainly will be required to go on "pelvic bedrest," and to avoid all penetration until after delivery.

 Diagnosis of placenta previa before week 20 can often be premature. In fact, one study found that 97% cases of early diagnosis do not end up being a case of complete previa by the date of delivery.  Another study has found, however, that an overlap of 25 mm or more at 20-23 weeks seems to be incompatible with later vaginal delivery. (see studies below)

Placenta Previa: Predisposing Factors

1. Women over 35 are three times more likely to have a placenta previa.
2. A large, thin placenta. These are more likely to cover the cervix simply because they take up more of the uterine surface.
3. Multiparity. Theoretically, the trophoblast seeks out a new area to implant during each pregnancy; if several pregnancies preceded this one, there will be less such areas in the uterine lining.
4. If the lining of the upper uterine segment is deficient, the placenta may spread out over more of the uterine wall in an effort to maintain an adequate blood supply.
5. Endometritis following a previous pregnancy.
6. Uterine scars. In one study, the rate of previa in an unscarred uterus was 0.26 percent, 0.65 percent after one cesarean, 1.8 percent after two, 3 percent after three, and 10 percent after four or more, a 38-fold increase.
7. Repeated pregnancies with short intervals in between.
8. A history of previa. Women with a history of previa are twelve times more likely to have a recurrence.
9. Multiple gestation, due to the large placental implantation site(s).
10. Any disturbance of the healthy formation of the uterine lining.
-Anne Frye, Holistic Midwifery Volume 1, Labrys Press, 1995. 

Studies on Placenta Previa


Placenta previa - 97% of early diagnoses are misdiagnosed.

Ultrasound screening and perinatal mortality: controlled trial of systematic one-stage screening in pregnancy. The Helsinki Ultrasound Trial.
Saari-Kemppainen A, Karjalainen O, Ylostalo P, Heinonen OP
Lancet 1990 Aug 18;336(8712):387-91

An overlap of 25 mm or more at 20-23 weeks seems to be incompatible with later vaginal delivery.

The relevance of placental location at 20-23 gestational weeks for prediction of placenta previa at delivery: evaluation of 8650 cases.
Becker RH, Vonk R, Mende BC, Ragosch V, Entezami M
Ultrasound Obstet Gynecol 2001 Jun;17(6):496-501


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