774: Stillbirth rates in relation to maternal age and race/ethnicity: A population-based study in the US

Abstract

Stillbirth complicates 1 in 160 pregnancies in the US. Two well established risk factors include advanced maternal age and non-Hispanic black race. We examined the association between maternal age and stillbirth across race. We performed a cross-sectional study of singleton births (20-44 weeks) in the US from 2015-17 utilizing Vital Statistics data. Stillbirth rates by maternal age (< 15, 15-19, 20-24, 25-29 [reference], 30-34, 35-39, 40-44, and 45-49 yrs) were examined overall and across self-reported maternal races. Missing covariate data were imputed. Associations were estimated from Cox proportional hazards regression models before and after adjustment for potential confounders. The role of unmeasured confounding in the effect measure (hazard ratio [HR] and 95% confidence interval [CI]) was evaluated. Of 11,463,054 singleton births in the US, the stillbirth (n=64,604) rate was 5.6/1000. More Hispanic (39.6%) and non-Hispanic black (31.5%) women delivered at age < 15 yrs compared to non-Hispanic white women (21.7%). The highest stillbirth rates were seen at the extremes of age (figure). Hispanic women had the lowest stillbirth rate at all ages. Non-Hispanic white women had similar rates at 30-44 yrs. Compared to women 25-29 yrs, the hazards of stillbirth among non-Hispanic white, non-Hispanic blacks, and Hispanic women < 15 yrs were 2.53 (95% CI 1.69, 3.80), 1.07 (95% CI 0.75, 1.53), and 1.75 (95% CI 1.11, 2.75) respectively. Hazard ratios increased with advancing age, and were 2.82 (95% CI 2.35, 3.38), 1.71 (95% CI 1.33, 2.20), and 2.99 (95% CI 2.26, 3.96) among non-Hispanic white, non-Hispanic black, and Hispanic women 45-49 yrs, respectively. Unmeasured confounding appeared to have little influence on associations. Stillbirth rates among women < 20 yrs were similar to rates among women ages 35-39 in their corresponding race/ethnicity. While the associations between maternal age and stillbirth appear smaller in magnitude among non-Hispanic blacks, their absolute rates are substantially higher compared to both non-Hispanic white and Hispanic women.