Association Between Prenatal Exposure To Traffic-Related Air Pollution And Preterm Birth In The Pelagie Mother-Child Cohort, Brittany, France. Does The Urban-Rural Context Matter ?

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Introduction: In urban settings, evidence that exposure to ambient air pollution during pregnancy may influence preterm birth (PTB) has accumulated. Conversely, this relation has hardly been investigated in rural areas where individuals' characteristics (demographic, socioeconomic and psychosocial factors) and environmental co-exposures may differ. We therefore examined the association between prenatal exposure to traffic-related air pollution and PTB among pregnant women from the PELAGIE mother-child cohort (Brittany, France, 2002-2006) living in urban and rural settings (1550 and 959 women, respectively). Methods: Women's residences were classified as either urban or rural using the French census bureau rural-urban continuum code. Nitrogen dioxide (NO2) concentrations at home addresses were estimated from adjusted land-use regression models. Associations between NO2 concentrations and PTB were assessed using logistic regressions. Results: Prevalence of PTB (3%) was similar among women living in urban and in rural settings. Better socioeconomic characteristics and health behaviours but more single-parent family situations were observed among urban women. NO2 exposure was on average 20.8 ± 6.6 µg.m-3 for women residing in urban areas and 18.8 ± 5.6 µg.m-3 for their rural counterparts. An increased risk of PTB was associated with the two highest terciles of NO2 concentration in urban areas (OR (16.43 -21.18 µg.m-3): 2.46, 95% CI: 1.06-5.81; OR(> 21.18 µg.m-3): 2.35, 1.02-5.42, respectively) but not in rural areas. Discussion: Our study conducted in a region with interspersed urban-rural areas, are in line with previous findings suggesting an increased risk of PTB associated with higher NO2 concentrations for women living in urban areas. The absence of association among their rural counterparts for whom exposure levels were similar, suggest that environmental mixtures and psychosocial inequalities might play a role in this heterogeneity.