Prenatal exposure to fine particulate matter composition and risk of cerebral palsy: A population-based retrospective cohort study in Ontario, Canada

Background: Existing literature suggests an association between prenatal exposure to fine particulate air pollution (PM_2.5) and cerebral palsy (CP). However, the impact of individual PM_2.5 components (SO₄²⁻, NH₄⁺, NO₃⁻, SS, BC, dust, OM) on CP risk remains unknown. Objective: To examine the associations between prenatal exposure to PM_2.5 components, and risk of CP among term births in Ontario, Canada. Methods: This was a retrospective cohort study that examined term births (gestational age ≥37 completed weeks) from April 2002 to December 2020. PM_2.5 total mass and composition measures were assigned to maternal residence at birth using satellite-based estimates and ground-level monitoring data. Cohort data were compiled using health administrative databases. Single-pollutant distributed lag cox proportional hazard models, with and without additional adjustment for PM_2.5 residuals, were used to investigate the associations between gestational exposures to PM_2.5 total mass and its components. Results: 2,193,427 mother-infant pairs were identified, of which 3907 were diagnosed with CP during the follow-up period. Increased risk of CP was found for SO₄²⁻ exposure during early pregnancy in both residual-adjusted (HR: 1.052, 95 % CI: 1.009–1.097, per IQR = 0.94 μg/m³), and non-adjusted models (HR: 1.050, 95 % CI: 1.007–1.095, per IQR = 0.94 μg/m³). The concentration-response relationship between the sensitive window found for SO₄²⁻ and CP risk (weeks 4–9 of gestation) showcased a supralinear pattern. Conclusions: Prenatal exposure to SO₄²⁻ may be associated with increased CP risk during the early pregnancy period. Associations between prenatal PM_2.5 total mass and composition exposure and CP risk should be further investigated.