Combinations of risk factors that have equivalent or greater stillbirth risk compared with chronic hypertension

To determine if pregnancy risk factors not currently used as indications for antenatal surveillance would, in combination, result in stillbirth risk greater than the risk associated with chronic hypertension (cHTN). This retrospective national cohort study using data abstracted from the National Center for Health Statistics and Centers for Disease Control and Prevention’s Division of Vital Statistics database included singleton, non-anomalous pregnancies delivered between 24 to 42 weeks gestation from 2015-2017. The primary outcome of interest was stillbirth. Exposures of interest included race/ethnicity, body mass index (BMI) classes, tobacco use, maternal age between 35-39 or ≥40 years. Each risk factor was stratified by established convention. Cox Proportional Hazard Regression analysis was performed to estimate stillbirth risk associated with each risk factor. The regression model also included cHTN, preeclampsia, diabetes and history of stillbirth in order to account for confounding effects from these risk factors. The coefficient for each of the risk factors was used to generate a statistical model for estimating stillbirth risk for various combinations of risk factors. Combinations with an equivalent or greater stillbirth risk compared to cHTN were identified. This study included 5,715,224 pregnancies, 11,424 (0.2%) of which were stillbirths. With all other risk factors at baseline, the hazard ratio (HR) for stillbirth associated with cHTN was 1.35, 95% CI [1.19, 1.54]. Any BMI categories ³25 kg/m2 combined with maternal age categories >35yo and smoking was associated with higher stillbirth risk compared with cHTN. Additionally, Black or Native Americans with less than a high school education combined with any BMI category ³25 kg/m2, maternal age >35 yo, or smoking had higher stillbirth risks (Table). Combinations of multiple risk factors may have greater stillbirth risk than cHTN alone. Antenatal surveillance should be performed in patients with these risk factor combinations.