Interpregnancy BMI change and risk of primary caesarean delivery.

We conducted a retrospective study using Missouri maternally linked cohort files (1989-2005). We examined the association between interpregnancy body mass index (BMI) change and risk of primary caesarean delivery. BMI was classified as normal (18.5-24.9 kg/m(2)) or obese (≥30.0 kg/m(2)). Interpregnancy BMI change was defined using the following categories: normal-normal, normal-obese, obese-normal and obese-obese. Logistic regression models were used to generate adjusted odds ratios (OR) and 95% confidence intervals (CI) for the risk of primary caesarean delivery in the second pregnancy. Elevated risks for caesarean delivery in the second pregnancy were noted for normal weight mothers becoming obese (OR = 1.41, 95% CI 1.26-1.57) and obese mothers maintaining their obese status across both pregnancies (OR = 1.75, 95% CI 1.65-1.87). Women with a reduction in BMI (obese-normal) had a risk level for primary caesarean section that was comparable with that of women with normal BMI status in both pregnancies.