Fine Particulate Air Pollution and Adverse Birth Outcomes: Effect Modification by Regional Nonvolatile Oxidative Potential

BACKGROUND: Prenatal exposure to fine particulate matter air pollution with aerodynamic diameter [Formula: see text] ([Formula: see text]) has been associated with preterm delivery and low birth weight (LBW), but few studies have examined possible effect modification by [Formula: see text] oxidative potential. OBJECTIVES: The aim of this study was to evaluate if regional differences in the oxidative potential of [Formula: see text] modify the relationship between [Formula: see text] and adverse birth outcomes. METHODS: A retrospective cohort study was conducted using 196,171 singleton births that occurred in 31 cities in the province of Ontario, Canada, from 2006 to 2012. Daily air pollution data were collected from ground monitors, and city-level [Formula: see text] oxidative potential was measured. We used random-effects meta-analysis to combine the estimates of effect from regression models across cities on preterm birth, term LBW, and term birth weight and used meta-regression to evaluate the modifying effect of [Formula: see text] oxidative potential. RESULTS: An interquartile increase ([Formula: see text]) in first-trimester [Formula: see text] was positively associated with term LBW among women in the highest quartile of glutathione (GSH)-related oxidative potential [[Formula: see text]; 95% confidence interval (CI): 1.10, 1.48], but not the lowest quartile ([Formula: see text]; 95% CI: 0.87, 1.14; [Formula: see text]). [Formula: see text] on the day of delivery also was associated with preterm birth among women in the highest quartile of GSH-related oxidative potential [[Formula: see text]; 95% CI: 1.01, 1.04], but not the lowest quartile [[Formula: see text]; 95% CI: 0.95, 1.00; [Formula: see text]]. Between-city differences in ascorbate (AA)-related oxidative potential did not significantly modify associations with [Formula: see text]. CONCLUSIONS: Between-city differences in GSH-related oxidative potential may modify the impact of [Formula: see text] on the risk of term LBW and preterm birth. https://doi.org/10.1289/EHP2535