Reevaluating the link between maternal age and stillbirth risk in the context of socioeconomic confounding

Abstract Previous research finds a J-shaped relationship between maternal age and stillbirth risk but often overlooks socioeconomic confounding, which may obscure underlying risk patterns, particularly among individuals with advanced maternal age (≥35 years) who tend to have greater socioeconomic advantage. Moreover, it is unclear whether the maternal age-stillbirth association differs by race/ethnicity, despite racial/ethnic differences in socioeconomic status. Using a fetuses-at-risk approach and restricted US vital statistics data from 2015–2019 (18,182,261 live births and 85,658 stillbirths), we examined the relationship between maternal age and stillbirth risk, assessed how adjustment for socioeconomic confounding influences this relationship, and evaluated whether race/ethnicity modifies the association. In the full sample, minimally adjusted models showed a J-shaped association between maternal age and stillbirth risk. However, after adjusting for socioeconomic confounding, the relationship shifted to a positive linear association. Before adjustment for socioeconomic confounding, the maternal-age stillbirth gradient appeared steeper among non-Hispanic Black, Hispanic, and American Indian/Alaska Native (AIAN) individuals compared to non-Hispanic White and Asian/Pacific Islander individuals. These patterns attenuated after full adjustment, except among AIAN individuals. Findings suggest that not adequately accounting for confounding by socioeconomic status may result in a misrepresentation of the relationship between maternal age and stillbirth risk.