Associations of pregnancy outcomes and PM_2.5 in a national Canadian study

Background: Numerous studies have examined associations between air pollution and pregnancy outcomes, but most have been restricted to urban populations living near monitors. Objectives: We examined the association between pregnancy outcomes and fine particulate matter in a large national study including urban and rural areas. Methods: Analyses were based on approximately 3 million singleton live births in Canada between 1999 and 2008. Exposures to PM_2.5 (particles of median aerodynamic diameter ≤ 2.5 μm) were assigned by mapping the mother’s postal code to a monthly surface based on a national land use regression model that incorporated observations from fixed-site monitoring stations and satellitederived estimates of PM_2.5. Generalized estimating equations were used to examine the association between PM_2.5 and preterm birth (gestational age < 37 weeks), term low birth weight (< 2,500 g), small for gestational age (SGA; < 10th percentile of birth weight for gestational age), and term birth weight, adjusting for individual covariates and neighborhood socioeconomic status (SES). Results: In fully adjusted models, a 10-μg/m³ increase in PM_2.5 over the entire pregnancy was associated with SGA (odds ratio = 1.04; 95% CI 1.01, 1.07) and reduced term birth weight (-20.5 g; 95% CI -24.7, -16.4). Associations varied across subgroups based on maternal place of birth and period (1999-2003 vs. 2004-2008). Conclusions: This study, based on approximately 3 million births across Canada and employing PM_2.5 estimates from a national spatiotemporal model, provides further evidence linking PM_2.5 and pregnancy outcomes.