Risk of first-stage and second-stage cesarean delivery by maternal body mass index among nulliparous women in labor at term.

OBJECTIVE To estimate in a cohort of nulliparous women in labor at term whether cesarean delivery rates are increased in first and second stages of labor in overweight and obese women and whether being overweight or obese is an independent risk factor for cesarean delivery. METHODS Nulliparous women recruited to the prospective Screening for Pregnancy Endpoints study who went into labor after 37 weeks of gestation were categorized according to ethnicity-specific body mass index (BMI) criteria as normal, overweight, or obese. Normal BMI was the referent. Multivariable analysis, adjusting for known confounders for obesity and cesarean delivery, was performed to estimate if being overweight or obese was associated with an increased risk of cesarean in labor (all cesarean deliveries and in first stage of labor). RESULTS Of 2,629 participants, 1,416 (54%) had normal BMIs, 773 (29%) were overweight, and 440 (17%) were obese. First-stage cesarean delivery was increased in overweight (n=149 [19%]) and obese (n=137 [31%]) women compared with normal-weight women (n=181 [13%; P<.001), whereas second-stage cesarean delivery was similar (normal BMI 76 [6.2%], overweight 45 [7.2%], obese 23 [7.6%], P=.87). Being overweight or obese was an independent risk factor for all cesarean deliveries in labor with adjusted odds ratio (OR) of 1.34 (95% confidence interval [CI] 1.07-1.67) and 2.51 (95% CI 1.94-3.25), respectively. Similarly, being overweight (adjusted OR 1.39; 95% CI 1.09-1.79) or obese (adjusted OR 2.89; 95% CI 2.19-3.80) was associated with increased cesarean delivery during the first stage. Risks of cesarean delivery were similar regardless of whether ethnicity-specific or World Health Organization (WHO) BMI criteria were used. CONCLUSION Among nulliparous women in labor at term, being overweight or obese by either WHO or ethnicity-specific BMI criteria is an independent risk factor for cesarean delivery in the first stage but not the second stage of labor. CLINICAL TRIAL REGISTRATION Australian New Zealand Clinical Trials Registry, www.anzctr.org.au, ACTRN12607000551493.