Effect of a low-lying placenta on delivery outcome

To evaluate delivery outcome in pregnancies with a low-lying placenta (within 2 cm of, but not covering, the internal os) that had been identified within 4 weeks of delivery. We examined the likelihood of a vaginal delivery and investigated the clinical significance of the placental edge to internal os measurement.

A retrospective chart review was performed for singleton pregnancies delivering in the third trimester with a low-lying placenta identified within 4 weeks of delivery. Outcome variables included type of delivery, maternal and neonatal hemoglobin levels, and umbilical artery pH levels.

Eighty-six patients met the study criteria of a low-lying placenta identified within 4 weeks of delivery. Forty-five of these patients were allowed to labor and, of these, 29 (64.4%) delivered vaginally. The vaginal delivery rate was 76.5% in patients with a placenta to cervical os distance of 1-2 cm, significantly greater than the rate of 27.3% in patients in whom the placenta was within 1 cm of the cervix (P = 0.0085). A maternal hemoglobin level below 8.0 g/dL was the most common morbidity associated with low-lying placenta. Analysis of morbidity observed did not clearly favor either elective Cesarean delivery or attempted vaginal delivery.

In this retrospective study, most laboring patients with a low-lying placenta were able to have a vaginal delivery with limited morbidity. The likelihood of a vaginal delivery was greater with increased placenta to cervical os distance. Further studies are needed to determine the clinical significance of the placenta to cervical os distance and the interval from scan to delivery.