Preconception, prenatal and early childhood exposure to green space and risk of neurodevelopmental delays: a national cohort study among Medicaid enrollees

Background: Exposure to green space is associated with children's mental health, but its impact on neurodevelopment has been underexplored, especially in socioeconomically disadvantaged populations. This study examined the link between exposure to green space before, during, and after pregnancy and neurodevelopmental delays in children enrolled in Medicaid. Methods: This cohort study of 1,841,915 mother–child pairs used data from the Medicaid Analytic Extract (MAX) from 2001 to 2014, with up to 14 years of follow-up. The population of pregnant women enrolled in Medicaid is characterized by younger age, racial and ethnic diversity, lower income levels, and includes individuals with disabilities. Green space exposure was measured using the Normalized Difference Vegetation Index (NDVI) at the maternal residential zip code level. We examined exposure to green space during the preconception, prenatal, and postnatal periods to capture critical developmental windows both separately and with mutual adjustment. Neurodevelopmental outcomes were identified using validated algorithms and included autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), learning disabilities, speech and language disorders, coordination disorders, intellectual disabilities, and behavioral disorders. We applied a stratified Cox model accounting for individual and area-level confounders and examined effect measure modification by urbanicity, child's race/ethnicity, and sex. Findings: The study found protective associations between green space exposure and most neurodevelopmental disorders. The strongest associations were seen for preconception exposure and intellectual disability (HR 0.66 [95 % CI: 0.48–0.95]), pregnancy exposure and ASD (HR 0.83 [95 % CI: 0.73–0.95]), and postnatal exposure for learning difficulties (HR 0.81 [95 % CI: 0.68–0.97]) per interquartile range (IQR = 0.12) increase in NDVI. The protective effects were stronger for Black/Hispanic children and for those living in urban areas. Interpretation: Green space exposure could benefit the children's neurodevelopment, with more significant benefits for the Black and Hispanic populations. Funding: National Institute of Environmental Health Sciences R01-ES034038.