Maternal Exposure to Particulate Air Pollution and Term Birth Weight: A Multi-Country Evaluation of Effect and Heterogeneity

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Abstract

Background: A growing body of evidence has associated maternal exposure to air pollution with adverse effects on fetal growth; however, the existing literature is inconsistent.

Objectives: We aimed to quantify the association between maternal exposure to particulate air pollution and term birth weight and low birth weight (LBW) across 14 centers from 9 countries, and to explore the influence of site characteristics and exposure assessment methods on between-center heterogeneity in this association.

Methods: Using a common analytical protocol, International Collaboration on Air Pollution and Pregnancy Outcomes (ICAPPO) centers generated effect estimates for term LBW and continuous birth weight associated with PM ₁₀ and PM _2.5 (particulate matter ≤ 10 and 2.5 µm). We used meta-analysis to combine the estimates of effect across centers (~ 3 million births) and used meta-regression to evaluate the influence of center characteristics and exposure assessment methods on between-center heterogeneity in reported effect estimates.

Results: In random-effects meta-analyses, term LBW was positively associated with a 10-μg/m ³ increase in PM ₁₀ [odds ratio (OR) = 1.03; 95% CI: 1.01, 1.05] and PM _2.5 (OR = 1.10; 95% CI: 1.03, 1.18) exposure during the entire pregnancy, adjusted for maternal socioeconomic status. A 10-μg/m ³ increase in PM ₁₀ exposure was also negatively associated with term birth weight as a continuous outcome in the fully adjusted random-effects meta-analyses (–8.9 g; 95% CI: –13.2, –4.6 g). Meta-regressions revealed that centers with higher median PM _2.5 levels and PM _2.5:PM ₁₀ ratios, and centers that used a temporal exposure assessment (compared with spatiotemporal), tended to report stronger associations.

Conclusion: Maternal exposure to particulate pollution was associated with LBW at term across study populations. We detected three site characteristics and aspects of exposure assessment methodology that appeared to contribute to the variation in associations reported by centers.

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Most cited references 37

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Ambient Air Pollution and Pregnancy Outcomes: A Review of the Literature

Radim J. Sram, Blanka Binkova, Jan Dejmek (posthumous) … (2005)

Over the last decade or so, a large number of studies have investigated the possible adverse effects of ambient air pollution on birth outcomes. We reviewed these studies, which were identified by a systematic search of the main scientific databases. Virtually all reviewed studies were population based, with information on exposure to air pollution derived from routine monitoring sources. Overall, there is evidence implicating air pollution in adverse effects on different birth outcomes, but the strength of the evidence differs between outcomes. The evidence is sufficient to infer a causal relationship between particulate air pollution and respiratory deaths in the postneonatal period. For air pollution and birth weight the evidence suggests causality, but further studies are needed to confirm an effect and its size and to clarify the most vulnerable period of pregnancy and the role of different pollutants. For preterm births and intrauterine growth retardation (IUGR) the evidence as yet is insufficient to infer causality, but the available evidence justifies further studies. Molecular epidemiologic studies suggest possible biologic mechanisms for the effect on birth weight, premature birth, and IUGR and support the view that the relation between pollution and these birth outcomes is genuine. For birth defects, the evidence base so far is insufficient to draw conclusions. In terms of exposure to specific pollutants, particulates seem the most important for infant deaths, and the effect on IUGR seems linked to polycyclic aromatic hydrocarbons, but the existing evidence does not allow precise identification of the different pollutants or the timing of exposure that can result in adverse pregnancy outcomes.

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A Cohort Study of Traffic-Related Air Pollution Impacts on Birth Outcomes

Michael Brauer, Cornel Lencar, Lillian Tamburic … (2008)

Background Evidence suggests that air pollution exposure adversely affects pregnancy outcomes. Few studies have examined individual-level intraurban exposure contrasts. Objectives 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) μm 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 26% increase in SGA [95% confidence interval (CI), 1.07–1.49] and an 11% (95% CI, 1.01–1.23) 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-μg/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. Conclusion Associations between traffic-related air pollution and birth outcomes were observed in a population-based cohort with relatively low ambient air pollution exposure.

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Statistical heterogeneity in systematic reviews of clinical trials: a critical appraisal of guidelines and practice.

Julian PT Higgins, Simon Thompson, Jonathan Deeks … (2002)

Heterogeneity between study results can be a problem in any systematic review or meta-analysis of clinical trials. Identifying its presence, investigating its cause and correctly accounting for it in analyses all involve difficult decisions for the researcher. Our objectives were: to collate recommendations on the subject of dealing with heterogeneity in systematic reviews of clinical trials; to investigate current practice in addressing heterogeneity in Cochrane reviews; and to compare current practice with recommendations. We review guidelines for those undertaking systematic reviews and examine how heterogeneity is addressed in practice in a sample of systematic reviews, and their protocols, from the Cochrane Database of Systematic Reviews. Advice to reviewers is on the whole consistent and sensible. However, examination of a sample of Cochrane protocols and reviews demonstrates that the advice is difficult to follow given the small numbers of studies identified in many systematic reviews, the difficulty of pre-specifying important effect modifiers for subgroup analysis or meta-regression and the unresolved debate concerning fixed versus random effects meta-analyses. There was disagreement between protocols and reviews, often either regarding choice of important potential effect modifiers or due to the review identifying too few studies to perform planned analyses. Guidelines that address practical issues are required to reduce the risk of spurious findings from investigations of heterogeneity. This may involve discouraging statistical investigations such as subgroup analyses and meta-regression, rather than simply adopting a cautious approach to their interpretation, unless a large number of studies is available. The notion of a priori specification of potential effect modifiers for a retrospective review of studies is ill-defined, and the appropriateness of using a statistical test for heterogeneity to decide between analysis strategies is suspect.

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Author and article information

Journal

Journal ID (nlm-ta): Environ Health Perspect

Journal ID (iso-abbrev): Environ. Health Perspect

Journal ID (publisher-id): EHP

Title: Environmental Health Perspectives

Publisher: National Institute of Environmental Health Sciences

ISSN (Print): 0091-6765

ISSN (Electronic): 1552-9924

Publication date (Electronic): 06 February 2013

Publication date (Print): March 2013

Volume: 121

Issue: 3

Pages: 267-373

Affiliations

[1 ]Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain

[2 ]Municipal Institute of Medical Research (IMIM-Hospital del Mar), Barcelona, Spain

[3 ]CIBER Epidemiologia y Salud Pública (CIBERESP), Spain

[4 ]National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland, USA

[5 ]School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, USA

[6 ]Department of Clinical and Experimental Medicine, University of Insubria, Varese, Italy

[7 ]University of British Columbia, School of Population and Public Health, Vancouver, British Columbia, Canada

[8 ]Department of Environmental Health, Emory University, Atlanta, Georgia, USA

[9 ]Institute for Risk Assessment Sciences, Utrecht University, Utrecht, the Netherlands

[10 ]Institute of Health & Society, Newcastle University, Newcastle upon Tyne, United Kingdom

[11 ]Department of Preventive Medicine, School of Medicine of the University of São Paulo, São Paulo, Brazil

[12 ]Department of Preventive Medicine, Ewha Womans University, Seoul, Republic of Korea

[13 ]Department of Occupational and Environmental Medicine, Inha University, Incheon, Republic of Korea

[14 ]Generation R Study Group, Erasmus Medical Center, Rotterdam, the Netherlands

[15 ]Urban Environment and Safety, TNO, Utrecht, the Netherlands

[16 ]Centre for Research, Evidence Management and Surveillance, Sydney, Australia

[17 ]South Western Sydney Local Health Districts, Sydney, Australia

[18 ]School of Public Health and Community Medicine, University of New South Wales, Sydney, Australia

[19 ]Department of Environmental Science, Policy, and Management, University of California–Berkeley, Berkeley, California, USA

[20 ]Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA

[21 ]Team of Environmental Epidemiology Applied to Reproduction and Respiratory Health, INSERM, and

[22 ]Grenoble University, U823, Institut Albert Bonniot, Grenoble, France

[23 ]School of Public Health, University of California–Berkeley, Berkeley, California, USA

[24 ]North Coast Area Health Service, Lismore, New South Wales, Australia

[25 ]University Centre for Rural Health–North Coast, University of Sydney, Sydney, Australia

[26 ]Department of Occupational and Environmental Health, Università di Milano, Milan, Italy

[27 ]Department of Public Health Sciences, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA

[28 ]Seattle Children’s Research Institute, University of Washington, Seattle, Washington, USA

[29 ]Centre for Health Services and Policy Research, University of British Columbia, Vancouver, Canada

[30 ]UMDNJ–Robert Wood Johnson Medical School, Piscataway, New Jersey, USA

[31 ]Center for Reproductive Health and the Environment, University of California–San Francisco, San Francisco, California, USA

Author notes

Address correspondence to P. Dadvand, CREAL, Barcelona Biomedical Research Park, Dr. Aiguader, 88, 08003 Barcelona, Spain. Telephone: 34 93 214 7317. E-mail: pdadvand@ 123456creal.cat

Article

Publisher ID: ehp.1205575

DOI: 10.1289/ehp.1205575

PMC ID: 3621183

PubMed ID: 23384584

SO-VID: d5f33fd2-ec94-4e1d-90d6-ec631479826e

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This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, properly cited.

Maternal Exposure to Particulate Air Pollution and Term Birth Weight: A Multi-Country Evaluation of Effect and Heterogeneity

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Abstract

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Pneumonia, sex, and the environment

Most cited references 37

Ambient Air Pollution and Pregnancy Outcomes: A Review of the Literature

A Cohort Study of Traffic-Related Air Pollution Impacts on Birth Outcomes

Statistical heterogeneity in systematic reviews of clinical trials: a critical appraisal of guidelines and practice.

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