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 = 50,416).

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 ≥16 kg 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 16 kg.