Does exposure to black carbon during pregnancy increase the risk of autism spectrum disorder? A cohort study from Southern Sweden

Black carbon (BC), a major component of fine particulate matter (PM_2.5), has been implicated in adverse neurodevelopmental outcomes, including autism spectrum disorders (ASD). While PM_2.5 has been associated with increased ASD risk, the specific role of BC remains uncertain. This study aimed to assess prenatal exposure to BC and risk for ASD development in a low exposure setting, using a large, high-quality register database, with disease diagnosis made by a single team. We used the Maternal Air Pollution in Southern Sweden cohort, encompassing nearly all births in the Malmö region, linked with ASD diagnoses. Exposure estimates included locally emitted PM_2.5 and BC, based on residential address during the entire pregnancy and for each trimester separately. Odds ratios were estimated with logistic regression models, adjusted for potential confounders. The final analytical cohort included 40,156 individuals. Associations between prenatal exposure to BC and ASD were observed in multiple models and across different trimesters, with an adjusted odds ratio (OR) of 1.17 (95 % CI: 0.97-1.41) per intra-quartile range (IQR) increase in BC exposure over the full pregnancy. For non-BC PM_2.5, the OR was 1.22 (95 % CI: 1.00-1.49) per IQR increase. This study utilised a large, high-quality register of births, matched to residential addresses and demographics factors, with a highly reliable disease outcome, against high-quality air pollution models. Positive trends were seen between BC exposure and ASD outcome, which were attenuated slightly, and becoming non-significant, when controlling for covariates. We observed stronger associations for PM_2.5 than BC. This study is novel in the precision of individual data, exposure and diagnosis, and is useful for future meta-analyses.