Pre-pregnant body mass index, gestational weight gain and the risk of operative delivery

Objective To estimate the risk of operative delivery according to maternal pre-pregnant body mass index (BMI) and gestational weight gain. Design Population-based pregnancy cohort study. Setting The Norwegian Mother and Child Cohort Study. Sample Term singleton deliveries in cephalic presentation, excluding preeclampsia, chronic hypertension, diabetes, gestational diabetes and placenta previa (n=50416). Methods Relative risks (RR) were obtained using general linear models. Main outcome measures RR of operative vaginal delivery and cesarean section. Results Overweight and obese women had an increased risk of cesarean section, strongest for women with a pre-pregnancy BMI >40 (RR: 3.4, 95% confidence interval (CI): 2.8-4.1). There was also an increased risk of vacuum extraction delivery for women with a pre-pregnancy BMI >40 (RR: 1.5, 95% CI: 1.04-2.2). Women with a gestational weight gain of 16kg had a significantly increased risk of forceps, vacuum extraction and cesarean section (RR: 1.2, 95% CI: 1.03-1.4, RR: 1.2, 95% CI: 1.1-1.23 and RR: 1.3, 95% CI: 1.26-1.4, respectively). Weight gain during pregnancy was significantly lower in obese women, but the children tended to be larger. Conclusions Obese women have an increased risk of operative delivery with vacuum extraction and cesarean section. Independently of pre-pregnancy BMI, we found an increased risk of operative intervention during delivery for women with gestational weight gain above 16kg.