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      Associations of Pregnancy Outcomes and PM 2.5 in a National Canadian Study


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          Numerous studies have examined associations between air pollution and pregnancy outcomes, but most have been restricted to urban populations living near monitors.


          We examined the association between pregnancy outcomes and fine particulate matter in a large national study including urban and rural areas.


          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 satellite-derived 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).


          In fully adjusted models, a 10-μg/m 3 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).


          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.


          Stieb DM, Chen L, Beckerman BS, Jerrett M, Crouse DL, Omariba DW, Peters PA, van Donkelaar A, Martin RV, Burnett RT, Gilbert NL, Tjepkema M, Liu S, Dugandzic RM. 2016. Associations of pregnancy outcomes and PM 2.5 in a National Canadian Study. Environ Health Perspect 124:243–249;  http://dx.doi.org/10.1289/ehp.1408995

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          Most cited references27

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          A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010

          The Lancet, 380(9859), 2224-2260
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            A new and improved population-based Canadian reference for birth weight for gestational age.

            Existing fetal growth references all suffer from 1 or more major methodologic problems, including errors in reported gestational age, biologically implausible birth weight for gestational age, insufficient sample sizes at low gestational age, single-hospital or other non-population-based samples, and inadequate statistical modeling techniques. We used the newly developed Canadian national linked file of singleton births and infant deaths for births between 1994 and 1996, for which gestational age is largely based on early ultrasound estimates. Assuming a normal distribution for birth weight at each gestational age, we used the expectation-maximization algorithm to exclude infants with gestational ages that were more consistent with 40-week births than with the observed gestational age. Distributions of birth weight at the corrected gestational ages were then statistically smoothed. The resulting male and female curves provide smooth and biologically plausible means, standard deviations, and percentile cutoffs for defining small- and large-for-gestational-age births. Large-for-gestational age cutoffs (90th percentile) at low gestational ages are considerably lower than those of existing references, whereas small-for-gestational-age cutoffs (10th percentile) postterm are higher. For example, compared with the current World Health Organization reference from California (Williams et al, 1982) and a recently proposed US national reference (Alexander et al, 1996), the 90th percentiles for singleton males at 30 weeks are 1837 versus 2159 and 2710 g. The corresponding 10th percentiles at 42 weeks are 3233 versus 3086 and 2998 g. This new sex-specific, population-based reference should improve clinical assessment of growth in individual newborns, population-based surveillance of geographic and temporal trends in birth weight for gestational age, and evaluation of clinical or public health interventions to enhance fetal growth. fetal growth, birth weight, gestational age, preterm birth, postterm birth.
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              Ambient air pollution, birth weight and preterm birth: a systematic review and meta-analysis.

              Low birth weight and preterm birth have a substantial public health impact. Studies examining their association with outdoor air pollution were identified using searches of bibliographic databases and reference lists of relevant papers. Pooled estimates of effect were calculated, heterogeneity was quantified, meta-regression was conducted and publication bias was examined. Sixty-two studies met the inclusion criteria. The majority of studies reported reduced birth weight and increased odds of low birth weight in relation to exposure to carbon monoxide (CO), nitrogen dioxide (NO(2)) and particulate matter less than 10 and 2.5 microns (PM(10) and PM(2.5)). Effect estimates based on entire pregnancy exposure were generally largest. Pooled estimates of decrease in birth weight ranged from 11.4 g (95% confidence interval -6.9-29.7) per 1 ppm CO to 28.1g (11.5-44.8) per 20 ppb NO(2), and pooled odds ratios for low birth weight ranged from 1.05 (0.99-1.12) per 10 μg/m(3) PM(2.5) to 1.10 (1.05-1.15) per 20 μg/m(3) PM(10) based on entire pregnancy exposure. Fewer effect estimates were available for preterm birth and results were mixed. Pooled odds ratios based on 3rd trimester exposures were generally most precise, ranging from 1.04 (1.02-1.06) per 1 ppm CO to 1.06 (1.03-1.11) per 20 μg/m(3) PM(10). Results were less consistent for ozone and sulfur dioxide for all outcomes. Heterogeneity between studies varied widely between pollutants and outcomes, and meta-regression suggested that heterogeneity could be partially explained by methodological differences between studies. While there is a large evidence base which is indicative of associations between CO, NO(2), PM and pregnancy outcome, variation in effects by exposure period and sources of heterogeneity between studies should be further explored. Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.

                Author and article information

                Environ Health Perspect
                Environ. Health Perspect
                Environmental Health Perspectives
                National Institute of Environmental Health Sciences
                19 June 2015
                February 2016
                : 124
                : 2
                : 243-249
                [1 ]Population Studies Division, Health Canada, Vancouver, British Columbia, Canada
                [2 ]Population Studies Division, Health Canada, Ottawa, Ontario, Canada
                [3 ]Geographic Information Health and Exposure Science Laboratory (GIS HEAL), School of Public Health, University of California, Berkeley, Berkeley, California, USA
                [4 ]Department of Environmental Health Sciences, Fielding School of Public Health, University of California, Los Angeles, Los Angeles, California, USA
                [5 ]Department of Sociology, University of New Brunswick, Fredericton, New Brunswick, Canada
                [6 ]Special Surveys Division, Statistics Canada, Ottawa, Ontario, Canada
                [7 ]Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
                [8 ]Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
                [9 ]Vaccine and Immunization Program Surveillance Division, Public Health Agency of Canada, Ottawa, Canada
                [10 ]Health Analysis Division, Statistics Canada, Ottawa, Ontario, Canada
                [11 ]Maternal, Child and Youth Health, Surveillance and Epidemiology Division, Public Health Agency of Canada, Ottawa, Ontario, Canada
                [12 ]Air Health Science Division, Health Canada, Ottawa, Ontario, Canada
                Author notes
                [* ]Address correspondence to D.M. Stieb, Population Studies Division, Health Canada, 445-757 West Hastings St.–Federal Tower, Vancouver, British Columbia, Canada, V6C 1A1. Telephone: (604) 666-3701. E-mail: dave.stieb@ 123456hc-sc.gc.ca

                Publication of EHP lies in the public domain and is therefore without copyright. All text from EHP may be reprinted freely. Use of materials published in EHP should be acknowledged (for example, “Reproduced with permission from Environmental Health Perspectives”); pertinent reference information should be provided for the article from which the material was reproduced. Articles from EHP, especially the News section, may contain photographs or illustrations copyrighted by other commercial organizations or individuals that may not be used without obtaining prior approval from the holder of the copyright.

                : 24 July 2014
                : 17 June 2015
                : 19 June 2015
                : 01 February 2016
                Children's Health

                Public health
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