Placenta previa/accreta and prior cesarean section.

TLDR

The study examined how the number of prior cesarean sections influences the risk of placenta previa and placenta accreta. Researchers retrospectively reviewed records of all patients diagnosed with placenta previa at a single institution from 1977 to 1983. Among 97,799 patients, placenta previa risk increased from 0.26% in unscarred uteri to 10% with four or more prior cesareans, and placenta accreta risk rose from 5% to 67% across the same groups, with age and parity having a smaller impact.

Abstract

To assess the relationship between increasing numbers of previous cesarean sections and the subsequent development of placenta previa and placenta accreta, the records of all patients presenting to labor and delivery with the diagnosis of placenta previa between 1977 and 1983 were examined. Of a total of 97,799 patients, 292 (0.3%) had a placenta previa. The risk of placenta previa was 0.26% with an unscarred uterus and increased almost linearly with the number of prior cesarean sections to 10% in patients with four or more. The effect of advancing age and parity on the incidence of placenta previa was much less dramatic. Patients presenting with a placenta previa and an unscarred uterus had a 5% risk of clinical placenta accreta. With a placenta previa and one previous cesarean section, the risk of placenta accreta was 24%; this risk continued to increase to 67% (two of three) with a placenta previa and four or more cesarean sections. Possible mechanisms and clinical implications are discussed.