Effect of pre-pregnancy body mass index on respiratory-related neonatal outcomes in women undergoing elective cesarean prior to 39 weeks

Objective: To examine the association between pre-pregnancy body mass index (BMI) and neonatal respiratory-related outcomes among women who underwent an elective cesarean section (CS). Methods: A retrospective cohort study was conducted using the Centers for Disease Control and Prevention (CDC)'s 2009-2013 period linked birth/infant death dataset. Women who had elective CSs at term were categorized by their pre-pregnancy BMI as normal, overweight, obese or morbidly obese. Odds ratios (OR) and 95% confidence intervals (CIs), adjusted for baseline characteristics, were calculated using multivariate logistic regression to estimate the neonatal risks in relation to maternal pre-pregnancy BMI. Results: Our cohort consisted of 717,080 women, of whom 39.9% had normal BMI, 27.0% were overweight, 25.7% obese and 7.4% morbidly obese. A dose-dependent relationship between maternal pre-pregnancy BMI and assisted ventilation was seen. Furthermore, infants born to morbidly obese women were at significantly increased risk for assisted ventilation over 6 h (OR 1.24, 95% CI 1.15-1.35) and admission to intensive care units (OR 1.17, 95% CI 1.13-1.21). Infant mortality rates were 4.2/1000 births for normal weight women, and 5.5/1000 births among the morbidly obese group (OR 1.43, 95% CI 1.25-1.64). Risk for adverse outcomes was increased with elective SC performed at earlier gestational age, and this effect was not modified by use of corticosteroids. Conclusion: Overweight and obese women are at particularly greater risk of adverse newborn outcomes when elective CSs are done before 39 weeks. In these women, elective CSs should be delayed until 39 weeks, as corticosteroid use did not eliminate this association.