Comparing exposure metrics in the relationship between PM2.5 and birth weight in California

Abstract

Although studies suggest that air pollution is linked to perinatal outcomes, the geographic characterization of exposure to pollution differs between the studies. We compared neighborhood-and county-level measures of air pollution exposure, while examining the association between particulate matter less than 2.5 mm in aerodynamic diameter (PM 2.5 ) and birth weight among full-term births in California in 2000. To reduce the effects of demographic variability, our analysis was limited to two populations of 8579 non-Hispanic white and 8114 Hispanic mothers who were married, between 20 and 30 years of age, completed at least a high school education, and gave birth for the first time. Measurements from the nearest monitor, and average and distance-weighted average of monitors within a 5-mile radius from each mother's residence (constituting neighborhood metrics) and the mean of monitors within each mother's county of residence were considered. PM 2.5 measurements, provided by the California Air Resources Board, were calculated to correspond to each mother's 9-month gestation period. Although metrics within the 5-mile radii and the county were highly correlated (r 2 ¼ 0.78), the county-level metric provided a stronger association between PM 2.5 and birth weight (b ¼ À4.04, 95% confidence interval ¼ À6.71, À1.37) than the metric for the average of all monitors within 5-miles (b ¼ À1.38, 95% confidence interval ¼ À3.36, 0.60) among non-Hispanic white mothers; similar results were observed among the Hispanic sample of mothers. Consequently, inferences from studies using different definitions of air pollution exposure may not be comparable.

Linkage of the US National Health Interview Survey to air monitoring data: An evaluation of different strategies

“…We found that differences in the geographic linkage method did not lead to large differences in the association between health status and PM 2.5 pollution. That the adjusted ORs calculated for the 5-mile study samples were somewhat smaller than those calculated using the broader exposure areas (Table 5) is consistent with the findings of Basu et al (2004) and does not support the hypothesis that more precise measurements lead to stronger associations. However, it is unclear whether the results in Table 5 are due to differences in study sample or differences in exposure assignment.…”

“…Willis et al (2003) conducted a re-analysis of the American Cancer Society Study (ACS) and found stronger associations using exposures calculated at the county level than at the original metropolitan area level. In contrast, Basu et al (2004) compared county-level pollution exposure to exposure based on averaging pollution measurements within 5 miles of a mother's residence to assess PM 2.5 exposure and birth weight; the results of this California study showed a stronger effect for the county level compared to the 5-mile exposure measure. The consequences of using different geographic units of analysis have also been compared in studies of neighborhood characteristics on health (Krieger et al, 2002).…”

“…The study by Basu et al (2004), on the other hand, used the same study cohort for both the county-level and 5-mile analyses. Whether the conclusions of Willis et al would have differed had all respondents been included in the county-level analysis is unknown.…”

Associations between prenatal exposure to air pollution, small for gestational age, and term low birthweight in a state-wide birth cohort

“…Multiple studies have reported the association of fine particulate matter (PM 2.5 ) with low birthweight and growth restriction. The results of these studies generally demonstrate positive associations with PM 2.5 either averaged over the full pregnancy period or averaged over specific trimesters or periods of pregnancy (Basu et al, 2004;Bell et al, 2007;Wilhelm and Ritz, 2005;Liu et al, 2007;Morello-Frosch et al, 2010;Parker et al, 2005;Rich et al, 2009). However, some studies have also reported null results (Brauer et al, 2008;Mannes et al, 2005;Darrow et al, 2011).…”

Health Effects of Fine Particulate Air Pollution: Lines that Connect

“…438 -444 The effects of air pollution on various other birth outcomes are substantially less well established and understood. Nevertheless, there are a growing number of contemporary studies that have evaluated potential links between air pollution and birth weight, [445][446][447][448][449][450][451][452][453][454][455][456] premature birth, 449,456 -458 fetal growth, 459 -461 intrauterine mortality, 462 birth defects, 463 and lymphocyte immunophenotypes in cord and maternal blood at delivery. 464 Recent reviews of the literature dealing with air pollution and these various birth outcomes 441,442,444 generally suggest that there may be effects of ambient PM air pollution on these outcomes but that these effects are not well understood.…”