Prepregnancy obesity and risk of stillbirth in viable twin gestations.

We sought to estimate the impact of prepregnancy obesity on demise of one or both fetuses in twin gestations. We performed a retrospective cohort study using the Missouri maternally linked cohort files (years 1989-2005). Prepregnancy obesity was defined as a BMI >or=30. Outcomes of interest were stillbirth (intrauterine fetal death at >or=20 weeks' gestation) and demise of one (partial loss) or both (complete loss) fetuses, regardless of the cause. We used Cox Proportional Hazards with correction for intracluster correlation to obtain risk estimates. The overall stillbirth rate for twin gestations was 15.5/1,000 (18.4/1,000 vs. 14.5/1,000 in obese and normal weight mothers, respectively; P = 0.02). The rate for complete fetal loss was higher in obese mothers (8.3/1,000 vs. 5.6/1,000; P = 0.01) but was comparable for partial fetal loss (19.1/1,000 for obese vs. 16.3/1,000 for normal weight mothers; P = 0.1). Adjusted estimates confirmed these findings (adjusted hazards ratio (AHR) and 95% confidence interval (CI) = 1.31 (1.02-1.68) for stillbirth; AHR = 1.59; CI = 1.01-2.51) for complete loss; and AHR = 1.21; CI = 0.91-1.62) for partial loss. Subanalysis conducted on stillbirth showed that the risk associated with obesity was only elevated for same-sex (AHR = 1.54; CI = 1.15-2.04) but not opposite-sex twins (0.99; CI = 0.56-1.75). Our findings may find utility in counseling of obese women with twin gestations.