Geographic disparities in birth outcomes: County-level investigation on PM_2.5 and low birth weight in the United States

Exposure to air pollution adversely affects health and is highly associated with birth outcomes. This study analyzes the relationship between air pollution and low birth weight (LBW; less than 2,500 g at birth) at the county level in the United States. Using the latest publicly available data from the County Health Rankings and Roadmaps across 3,027 counties and equivalents, simple and quantile regression analyses were conducted to test the association between the average daily density of fine particulate matter (PM_2.5) and LBW. The LBW data were from 2016 to 2022 from the National Center for Health Statistics and PM_2.5 data were obtained from Environmental Public Health Tracking Network from 2019. We controlled for key covariates. Simple regression found that PM_2.5 (p <.001) and children in poverty (p <.001) were positively associated with LBW, while rural population (p <.001) was negatively associated. Quantile regression results showed that PM_2.5 was associated at 10th (p =.001) and 50th quantiles (p <.001), but not 90th quantile (p =.32), implying that air pollution may play a more pronounced role in counties with lower to moderate LBW rates, whereas counties with highest LBW may be driven by other socioeconomic factors such as children in poverty (p <.001) and uninsured population (p =.01). The findings highlight the strong link between air pollution and LBW which could have long-term health consequences. The differential associations of PM_2.5 and LBW across the LBW distribution have important implications for potential interventions that may require tailored approach to risk profiles of the geography.