County sanctuary policies and birthweight among immigrant birthing people across multilevel immigration policy climates in the United States, 2012–2020: a repeat cross-sectional study

BACKGROUND: County governments are increasingly active in immigration-related policymaking, yet the impact of these policies on immigrant health remains largely unknown. Our objective was to evaluate differences in birth weight among births to foreign-born people conceived in 2012-2020 by adoption of a county-level sanctuary policy and assess potential effect modification by other levels of immigration governance. METHODS: We conducted a multilevel repeat cross-sectional design using United States natality data. We included live births to foreign-born people conceived between 2012 and 2021. The primary exposure was county sanctuary policy (time-varying, present or absent during the conception year). We further assessed effect modification by active county 287 g agreement, state driver's licence law (present or absent during the conception year) or federal policy regime (second Obama administration vs first Trump administration). We used models including county fixed effects to estimate differences in birth weight, in grams, associated with county-level adoption of a sanctuary policy, controlling for individual and county covariates. We further examine effect modification by county, state and federal immigration policy climate. RESULTS: We included 4 422 562 live births, with a mean birth weight of 3286 grams (55.4% Hispanic, 19.0% Asian). Adopting a sanctuary policy was associated with a 9 g difference in birth weight (CI 5.7 to 12.4) adjusting for covariates. Results did not vary meaningfully by federal or state policy climate. This association was larger in counties with a concurrent 287 g agreement (17.2 g, CI 11.4 to 23.1, p-value: 0.0013). CONCLUSIONS: County-level sanctuary policies may buffer effects of negative concurrent policies.