Objective  To examine the effect of pre-pregnancy body mass index (BMI) for Chinese women on adverse pregnant outcomes in Wuhan municipality, China.

  Methods  We conducted a population-based cohort study in Wuhan, China among 76 709 pregnant women having singleton deliveries and their newborns during June 2011 to June 2013. Logistic regression model was used to estimate associations of pre-pregnant BMI with adverse birth outcomes.

  Results  Compared with the normal weight women, the lean women were more likely to have spontaneous vaginal delivery (odds ratio OR = 1.25, 95% confidence interval 95% CI: 1.20 – 1.30); whereas the overweight/obese women were less likely to have spontaneous vaginal delivery (OR = 0.52, 95% CI: 0.48 – 0.56); a significantly higher odd of cesarean section (OR = 1.94, 95% CI: 1.80 – 2.08) was noted among the overweight/obese women but a significantly lower odd of cesarean section (OR = 0.80, 95% CI: 0.77 – 0.83) was revealed among the lean women. In contrast to that among the normal weight women, the risk of operative vaginal delivery was significantly higher (OR = 1.33, 95% CI: 1.02 – 1.73) among the lean women but significantly lower among the overweight/obese women (OR = 0.56, 95% CI: 0.32 – 0.96). No significant associations of pre-pregnant BMI were found with Apgar score of less than 7 at one minute or at 5 minutes and with asphyxia neonatorum. In comparison wih the normal weight women, both the overweight/obese and lean women were significantly more likely to have preterm delivery (OR = 1.29, 95% CI: 1.14 – 1.46 and OR = 1.37, 95% CI: 1.24 – 1.51); the overweight/obese women were more likely (OR = 2.36, 95% CI: 2.15 – 2.59) but the lean women were less likely (OR = 0.51, 95% CI: 0.46 – 0.56) to give a birth to a macrosomia. However, no significant association was observed between pre-pregnant BMI and low birth weight of the neonates.

  Conclusion  Maternal pre-pregnancy overweight/obese has significant impact on the occurrence of spontaneous vaginal delivery, cesarean section, preterm delivery, and macrosomia based on the body mass index criterion for Chinese adults.