Interpregnancy body mass index changes and risk of stillbirth.

BACKGROUND/AIMS: To examine the association between interpregnancy body mass index (BMI) change and stillbirth. METHODS: Retrospective study using Missouri maternally linked cohort files (1978-2005). A total of 218,389 women were used in the analysis. BMI was classified as: underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), or obese (≥30.0). Weight change was defined based on BMI category (i.e. normal-normal, normal-obese, etc.). Cox proportional hazard regression models were used to generate adjusted hazard ratios (HR) and 95% CI for the risk of stillbirth in the second pregnancy. RESULTS: Significant findings were associated with interpregnancy BMI changes involving overweight mothers becoming obese (HR = 1.4, 95% CI 1.1-1.7), normal-weight mothers becoming overweight (HR = 1.2, 95% CI 1.0-1.4) or obese (HR = 1.5, 95% CI 1.1-2.1), or obese mothers maintaining their obesity status across the two pregnancies (HR = 1.4, 95% CI 1.2-1.7). Other weight change categories did not show significant risk elevation for stillbirth. CONCLUSIONS: BMI change appears to play an important role in subsequent stillbirth risk.