Association Of Gestational Exposure to Black Carbon and Birth Weight: Evidence From Denmark and Sweden

<bold>Background:</bold> Air pollution has been linked to reduced birth weight, but the association with black carbon (BC) remains insufficiently explored. This study examined the association of gestational exposure BC with birth weight outcomes. <bold>Method:</bold> We analyzed data from all singleton births in Denmark (DK, 1998–2016; n=1,058,906) and Scania, Sweden (SE, 2000–2009; n=43,676). BC and fine particulate matter (PM_2.5) were estimated by using high-resolution dispersion models based on maternal residential addresses during pregnancy. Linear, Logistic, and Poisson regression models were employed to assess the associations of BC with birth weight, low birth weight (LBW), and small for gestational age (SGA), adjusting for spatiotemporal and individual-level covariates. Effect modification by gender, mothers’ age, and socioeconomic status (SES) were examined. <bold>Results:</bold> Gestational exposure to BC was associated with birth weight and SGA risk: interquartile range (0.34 μg/m³ in DK, and 0.25 μg/m³ in SE) increase in BC was associated with -6.39 g (95% CI: -7.43, -5.34) and -9.41 g (-17.05, -1.78) decrease in birth weight and relative risk of 1.01 (1.00, 1.02) and 1.09 (1.02, 1.18) for SGA in DK and SE, respectively. No association was observed with LBW. After further adjustment for PM_2.5, the associations were attenuated but remained borderline significant for both birth weight and SGA, in both cohorts. Associations of BC with birth weight in DK were stronger in boys, young mothers, and mothers with low SES. <bold>Conclusion:</bold> Our findings suggest that BC adversely affects birth weight, suggestively independent of PM_2.5, and add important new evidence supporting the regulation of BC in addition to PM_2.5.