Study population
We identified probands (stillbirth cases; n=9,404) and their parents’ FDRs (n=73,339), SDRs (n=128,083) and TDRs (n=300,536), as well as probands (live birth controls; n=18,808) and their parents’ FDRs (n=166,188), SDRs (n=258,103) and TDRs (n=608,803) (Figure S1and Table S1 ). The rate of stillbirth among 1,903,782 births that occurred between 1978 and 2019 in the state of Utah was 0.5%, comparable rate to that of high-income countries (0.6%).1 The proportion of male infant sex slightly differed between cases (n=4,735; 50.4%) and controls (n=9,778; 52.0%). The median (IQR) birth weight in grams was 1,145 (440-2,567) in cases and 3,340 (3,020-3,646) in controls. The median (IQR) gestational ages of cases and controls were 29 (23-36) and 39 (38-40) weeks, respectively. The study population was comprised mostly of non-Hispanic Whites (66.0% cases and 73.0% controls). There was higher representation of non-Hispanic Blacks (0.7% vs 0.3%) and Hispanics (24.5% vs 21.2%) in cases than controls, respectively. Paternal demographic factors followed a similar pattern with a lower proportion of non-Hispanic Whites (60.6% vs 69.7%) and higher numbers of non-Hispanic Blacks (0.8% vs 0.5%) in cases compared to controls, respectively. Cases had lower maternal educational attainment (post-college 4.5% vs 7.1%), fewer prenatal visits (9 vs 11) and slightly higher pre-pregnancy body-mass-index (25.7 vs 24.7 kg/m2) than controls. Maternal comorbidities were more common among cases than controls, with higher rates of chronic hypertension (1.0% vs 0.6%), hypertensive disorder of pregnancy (12.4% vs 9.9%) and pregestational diabetes (1.6% vs 0.6%). Major congenital anomalies of the fetus were more common among cases than controls (7.3% vs. 0.8%).