Risk factors for classical hysterotomy by gestational age.

Objective: To examine the likelihood of classical hysterotomy across preterm gestational ages and to identify factors that increase its occurrence.

Methods: This is a secondary analysis of a prospective observational cohort collected by the Maternal-Fetal Medicine Network of all women with singleton gestations who underwent a cesarean delivery with a known hysterotomy. Comparisons were made based on gestational age. Factors thought to influence hysterotomy type were studied, including maternal age, body mass index, parity, birth weight, small for gestational age (SGA) status, fetal presentation, labor preceding delivery, and emergent delivery.

Results: Approximately 36,000 women were eligible for analysis, of whom 34,454 (95.7%) underwent low transverse hysterotomy and 1,562 (4.3%) underwent classical hysterotomy. The median gestational age of women undergoing a classical hysterotomy was 32 weeks and the incidence peaked between 24 0/7 weeks and 25 6/7 weeks (53.2%), declining with each additional week of gestation thereafter (P for trend <.001). In multivariable regression, the likelihood of classical hysterotomy was increased with SGA (n=258; odds ratio [OR] 2.71; confidence interval [CI] 1.78-4.13), birth weight 1,000 g or less (n=467; OR 1.51; CI 1.03-2.24), and noncephalic presentation (n=783; OR 2.03; CI 1.52-2.72). The likelihood of classical hysterotomy was decreased between 23 0/7 and 27 6/7 weeks of gestation and after 32 weeks of gestation when labor preceded delivery, and increased between 28 0/7 and 31 6/7 weeks of gestation and after 32 weeks of gestation by multiparity and previous cesarean delivery. Emergent delivery did not predict classical hysterotomy.

Conclusions: Fifty percent of women at 23-26 weeks of gestation who undergo cesarean delivery have a classical hysterotomy, and the risk declines steadily thereafter. This likelihood is increased by fetal factors, especially SGA and noncephalic presentation.

Level Of Evidence: : II.