Maternal Weathering and Infant Health: Understanding Low Birth Weight and Preterm Birth Among American Indians.

American Indian infants have heightened rates of low birth weight (LBW) and preterm birth (PTB) in the United States. This study aims to evaluate variation by maternal age in racial disparities in these outcomes, indicative of birth risk weathering. Potential mechanisms of these disparities are also considered. We conducted a cross-sectional study of births occurring between 2014 and 2022 to Montana residents who self-identified as non-Hispanic White (NHW) or American Indian/Alaskan Native (AI/AN), using Montana birth certificate data. Logistic regression models were used to examine mediators of the association between AI/AN identity and experiencing a PTB (< 37 weeks gestation) and LBW outcome (< 2500 g at birth). Age-interactions tested the weathering hypothesis of maternal age variation in health disparities among AI/AN people. Four mediator variables were considered: pregnancy health risk, adequacy of prenatal care, distance to deliver, and prenatal smoking. Findings indicate that AI/AN individuals had heightened rates of PTB and LBW relative to NHWs (41% and 15% higher odds, respectively). Disparities are larger at older ages. The indirect effects of pregnancy health risk, adequacy of prenatal care, distance to deliver, and prenatal smoking partially explains the association between AI identity and outcomes; but age-graded disparities persist, particularly for PTB. Findings illustrate the importance of addressing maternal social determinants of health that may increase stress during the perinatal period, including by addressing barriers to accessing culturally responsive and safe prenatal care.