A cohort study of traffic-related air pollution impacts on birth outcomes.
BACKGROUND
Evidence suggests that air pollution exposure adversely affects pregnancy outcomes. Few studies have examined individual-level intraurban exposure contrasts.


OBJECTIVE
We evaluated the impacts of air pollution on small for gestational age (SGA) birth weight, low full-term birth weight (LBW), and preterm birth using spatiotemporal exposure metrics.


METHODS
With linked administrative data, we identified 70,249 singleton births (1999-2002) with complete covariate data (sex, ethnicity, parity, birth month and year, income, education) and maternal residential history in Vancouver, British Columbia, Canada. We estimated residential exposures by month of pregnancy using nearest and inverse-distance weighting (IDW) of study area monitors [carbon monoxide, nitrogen dioxide, nitric oxide, ozone, sulfur dioxide, and particulate matter < 2.5 (PM2.5) or < 10 (PM10) microm in aerodynamic diameter], temporally adjusted land use regression (LUR) models (NO, NO2, PM2.5, black carbon), and proximity to major roads. Using logistic regression, we estimated the risk of mean (entire pregnancy, first and last month of pregnancy, first and last 3 months) air pollution concentrations on SGA (< 10th percentile), term LBW (< 2,500 g), and preterm birth.


RESULTS
Residence within 50 m of highways was associated with a 22% (95% CI, 0.81-1.87) [corrected] increase in LBW. Exposure to all air pollutants except O3 was associated with SGA, with similar odds ratios (ORs) for LUR and monitoring estimates (e.g., LUR: OR = 1.02; 95% CI, 1.00-1.04; IDW: OR = 1.05; 95% CI, 1.03-1.08 per 10-microg/m3 increase in NO). For preterm births, associations were observed with PM2.5 for births < 37 weeks gestation (and for other pollutants at < 30 weeks). No consistent patterns suggested exposure windows of greater relevance.


CONCLUSIONS
Associations between traffic-related air pollution and birth outcomes were observed in a population-based cohort with relatively low ambient air pollution exposure.
Brauer
Michael
M
School of Environmental Health, The University of British Columbia, 2206 East Mall, Vancouver BC V6T1Z3 Canada. brauer@interchange.ubc.ca
Lencar
Cornel
C
Tamburic
Lillian
L
Koehoorn
Mieke
M
Demers
Paul
P
Karr
Catherine
C
D000393:Air Pollutants / Q000032:analysis* / Q000633:toxicity; D001724:Birth Weight; D001955:British Columbia / Q000453:epidemiology; D015331:Cohort Studies; D004784:Environmental Monitoring; D062665:Epidemiological Monitoring; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016017:Odds Ratio; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D018570:Risk Assessment; D001335:Vehicle Emissions / Q000032:analysis / Q000633:toxicity*
D000393:Air Pollutants; D001335:Vehicle Emissions