The joint effects of obesity and pregestational diabetes on the risk of stillbirth

Objective: Obesity and pregestational diabetes (PGDM) may interact to further increase the risk of stillbirth than either risk factors independently. The objective of this study was to determine the risk of stillbirth in pregnancies complicated by both conditions. Method: This was a retrospective cohort analysis of singleton nonanomalous births using the updated Texas vital records database between 2006 and 2014. Gestational diabetes and hypertensive diseases were additionally excluded from analysis. Analysis was stratified into 10 strata based on BMI class: underweight, normal weight, overweight, obese and morbidly obese, and PGDM. Furthermore, gestational age was stratified into the four periods for analysis: 24–33, 34–36, 37–39, and 40–42 weeks. The rate of stillbirth per 10,000 pregnancies were calculated for each stratum. The risks of stillbirth associated with each BMI class and PGDM were compared to normal weight nondiabetic pregnancies for each gestational period using proportional hazard regression models. Result: After all exclusions, 3,097,123 births remained for analysis, including 5997 stillbirths. The overall rate of stillbirth increased from 15.0 per 10,000 pregnancies in normal weight pregnancies to 26.7 per 10,000 pregnancies in the morbidly obese group. The rate of stillbirth further increased with coexistence of PGDM to 119.9 per 10,000 pregnancies in the normal weight group and 209.8 per 10,000 pregnancies in the morbidly obese group. Compared to normal weight nondiabetic pregnancies the overall adjusted hazard ratio (aHR) of stillbirth associated with morbid obesity without PGDM was 1.57 [1.38, 1.79]. However, when further complicated by PGDM, the aHR was 6.67 [5.05, 8.81] in normal weight pregnancies and 12.86 [9.36, 17.67] in morbidly obese pregnancies. The highest risk of stillbirth was seen between 37 and 39 weeks, when the aHR in the diabetic normal weight group was 9.63 [5.65, 16.40] and the aHR in the diabetic morbidly obese group was 25.34 [15.58, 41.22]. Conclusion: PGDM and obesity both independently increased the risk of stillbirth. The joint effect of obesity and PGDM is stronger than the summation or multiplication of the individual effects of each risk factor.