759: The interaction between obesity and pregestational diabetes on the risk of stillbirth

Abstract

stratified into the following four periods for analysis: 24-33 weeks, 34-36 weeks, 37-40 weeks and 40-42 weeks. The risks of stillbirth associated with each BMI class was compared to normal weight pregnancies for each gestational period using proportional hazard regression models. The indirect effect of obesity on stillbirth mediated through GDM and GHTN were then estimated. The ratio of the indirect effect to direct effect provided an estimate of the role these factors played in the causal pathway between obesity and stillbirth. RESULTS: After all exclusions 3,279,846 births remained for analysis, including 11,023 stillbirths. The effect of GDM in the causal pathway to stillbirth was similar for all BMI classes and peaked between 37-39 weeks. Between 37-39 weeks, the effect of BMI on stillbirth mediated through GDM ranged from 56% in obesity class II to 64% in the extreme obesity group. Whereas between 40-42 weeks, the mediated effects through GDM ranged from 33% in the extreme obesity group to 49% in obesity class II. In contrast, the stillbirth risk mediated through GHTN increased with BMI class and peaked between 40-42 weeks. Between 37-39 weeks, the risk of stillbirth mediated through GHTN was 22% in the overweight group, and increased with BMI to 49% in the extreme obesity group. Whereas between 40-42 weeks, the mediated effects through GHTN increased from 30% in the overweight group to 81% in the extreme obesity group. CONCLUSION: GDM and GHTN are both significant mediators in the causal pathway between BMI and stillbirth, although at different gestational periods. GDM had the strongest effect in the early term period; whereas GHTN had the greatest effect in the late term period.