Air pollution and birth outcomes: a systematic review.
ABSTRACT Several mechanisms are suspected to underlie adverse birth outcomes among mothers exposed to air pollutants, including inflammation, direct toxic effects on fetuses and the placenta, displacement of the oxygen-hemoglobin dissociation curve, and formation of DNA adducts.
To systematically review the association between air pollutants and birth outcomes of low birth weight (LBW), preterm (PTB) and small for gestational age (SGA) births.
Electronic databases and bibliographies of identified articles were searched for English language studies reporting on birth outcomes. Included studies were assessed for risks of bias in the selection, exposure assessment, confounder adjustment, analyses, outcomes assessment, and attrition. Unadjusted and adjusted estimates from included studies were extracted. Methodological differences between the studies were evaluated.
A total of 41 studies, mostly with a moderate risk of biases due to indirect assessment methods employed, met the eligibility criteria. Exposure to sulphur dioxide was associated with PTB, exposure to fine particulate matter (PM) of ≤2.5 μM was associated with LBW, PTB and SGA births, and exposure to coarse PM of ≤10 μM was associated with SGA births. The evidence for nitrous oxide, nitrogen dioxide, ozone and carbon monoxide was inconclusive.
Reported associations, and lack thereof, between individual air pollutants and birth outcomes have differed across published studies. This heterogeneity and/or absence of association may be due to difficulty in quantifying exposure, method of ascertainment, time of measurement and collinearity between pollutants. Important future research directions include developing improved methods to detect the duration and intensity of exposure, including entire populations, as well as performing well-designed nested studies that ascertain complete outcomes, avoiding residual confounding, and adjusting for residential mobility.
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ABSTRACT: Prenatal traffic-related air pollution exposure is linked to adverse birth outcomes. However, modifying effects of maternal body mass index (BMI) and infant sex remain virtually unexplored. We examined whether associations between prenatal air pollution and birth weight differed by sex and maternal BMI in 670 urban ethnically mixed mother-child pairs. Black carbon (BC) levels were estimated using a validated spatio-temporal land-use regression (LUR) model; fine particulate matter (PM2.5) was estimated using a hybrid LUR model incorporating satellite-derived Aerosol Optical Depth measures. Using stratified multivariable-adjusted regression analyses, we examined whether associations between prenatal air pollution and calculated birth weight for gestational age (BWGA) z-scores varied by sex and maternal pre-pregnancy BMI. Median birth weight was 3.3±0.6kg; 33% of mothers were obese (BMI ≥30kg/m(3)). In stratified analyses, the association between higher PM2.5 and lower birth weight was significant in males of obese mothers (-0.42 unit of BWGA z-score change per IQR increase in PM2.5, 95%CI: -0.79 to -0.06) ( PM2.5×sex×obesity Pinteraction=0.02). Results were similar for BC models (Pinteraction=0.002). Associations of prenatal exposure to traffic-related air pollution and reduced birth weight were most evident in males born to obese mothers. Copyright © 2014 Elsevier Inc. All rights reserved.Environmental Research 01/2015; 137C:268-277. · 3.95 Impact Factor
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ABSTRACT: Air pollution has been linked to gestational diabetes mellitus (GDM) but no studies have evaluated impact of preconception and early pregnancy air pollution exposures on GDM risk. Electronic medical records provided data on 219,952 singleton deliveries to mothers with (n=11,334) and without GDM (n=208,618). Average maternal exposures to particulate matter (PM) ≤ 2.5μm (PM2.5) and PM2.5 constituents, PM ≤ 10μm (PM10), nitrogen oxides (NOx), carbon monoxide, sulfur dioxide (SO2) and ozone (O3) were estimated for the 3-month preconception window, first trimester, and gestational weeks 1-24 based on modified Community Multiscale Air Quality models for delivery hospital referral regions. Binary regression models with robust standard errors estimated relative risks (RR) for GDM per interquartile range (IQR) increase in pollutant concentrations adjusted for study site, maternal age and race/ethnicity. Preconception maternal exposure to NOX (RR=1.09, 95% CI: 1.04, 1.13) and SO2 (RR=1.05, 1.01, 1.09) were associated with increased risk of subsequent GDM and risk estimates remained elevated for first trimester exposure. Preconception O3 was associated with lower risk of subsequent GDM (RR=0.93, 0.90, 0.96) but risks increased later in pregnancy. Maternal exposures to NOx and SO2 preconception and during the first few weeks of pregnancy were associated with increased GDM risk. O3 appeared to increase GDM risk in association with mid-pregnancy exposure but not in earlier time windows. These common exposures merit further investigation. Published by Elsevier Inc.Environmental Research 01/2015; 137C:316-322. · 3.95 Impact Factor
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ABSTRACT: Prenatal exposure to ambient air pollutants might cause adverse birth outcomes; however, there have been few studies in which the association between air pollution and preterm birth was examined after stratifying by pregnancy complications. We conducted a population-based case-control study of 1,510,064 singleton births from the Taiwanese birth registry during 2001-2007. Of the total of 1,510,064 births, we designated all 86,224 preterm births as the case group and then randomly selected an additional 344,896 from the remaining births (equivalent to 4 full-term births for every 1 preterm birth) as the control sample. We used an inverse distance weighting approach to calculate an average exposure parameter for air pollutants. The adjusted odds ratio for preterm birth per 10-ppb increase in ozone was 1.12 (95% confidence interval: 1.01, 1.23) for women with gestational diabetes mellitus who were exposed in the third trimester and 1.02 (95% confidence interval: 1.01, 1.03) for women without gestational diabetes (P for interaction <0.001). These findings suggest that exposure to ozone in pregnancy is associated with an increased risk of preterm birth, particularly for women who have gestational diabetes mellitus. © The Author 2015. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: email@example.com.American Journal of Epidemiology 02/2015; · 4.98 Impact Factor