Academic journal article Environmental Health Perspectives

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

Academic journal article Environmental Health Perspectives

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

Article excerpt

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 P[M.sub.10] and P[M.sub.2.5] (particulate matter [less than or equal to] 10 and 2.5 [micro]m). 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-[micro]g/[m.sup.3] increase in P[M.sub.10] [odds ratio (OR) = 1.03; 95% CI: 1.01, 1.05] and P[M.sub.2.5] (OR = 1.10; 95% CI: 1.03, 1.18) exposure during the entire pregnancy, adjusted for maternal socioeconomic status. A 10-[micro]g/[m.sup.3] increase in [PM.sub.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 P[M.sub.2.5] levels and P[M.sub.2.5]:P[M.sub.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.

KEY WORDS: air pollution, fetal growth, heterogeneity, ICAPPO, low birth weight, meta-analysis, meta-regression, multi-center study, particulate matter, pregnancy. Environ Health Perspect 121:367-373 (2013). http://dx.doi.org/10.1289/ehp.1205575 [Online 6 February 2013]

The developing fetus is known to be susceptible to environmental insults (Stillerman et al. 2008). A growing body of evidence has associated maternal exposure to ambient air pollution with a range of adverse pregnancy outcomes including low birth weight (LBW), intra-uterine growth retardation, preterm birth, stillbirth, and congenital anomalies (Glinianaia et al. 2004; Sapkota et al. 2010; Sram et al. 2005; Vrijheid et al. 2011). However, notable inconsistencies among the findings of these studies (Parker and Woodruff 2008; Parker et al. 2011; Woodruff et al. 2009) have hindered the ability of policy makers to incorporate the research evidence into policy.

Discrepancies among previous studies may reflect genuine differences in the study settings, may be a consequence of specific biases, or may arise from differences in study designs and exposure assessments (Parker and Woodruff 2008; Woodruff et al. 2009). Study setting characteristics that may contribute to variation in reported associations include the demographic characteristics of the study population, the major sources of pollutants, the size distribution of particulate pollutants [e.g., P[M.sub.2.5]:P[M.sub.10] ratio (particulate matter [less than or equal to] 2.5 and 10 [micro]m)], maternal time-activity patterns, the study period, the degree of confounding by socioeconomic status (SES), and the underlying prevalence of adverse pregnancy outcomes. Relevant study design characteristics include the sources of data for feto-maternal characteristics (e.g. …

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