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Air Pollution and Preterm Birth in Mexico City, Mexico (1992–2002)

Davis, B M*; O’Neill, M S*; Sánchez, B S*; Escobar, J D*; Ettinger, A S; Mercado-García, A; Hernández-Avila, M; Hu, H*; Téllez-Rojo, M M

doi: 10.1097/
Abstracts: ISEE 20th Annual Conference, Pasadena, California, October 12–16, 2008: Contributed Abstracts

*University of Michigan School of Public Health, Ann Arbor, MI, USA; †Harvard School of Public Health, Boston, MA, USA; and ‡National Institute of Public Health, Cuernavaca, Mexico.

Work supported by the Department of Environmental Health Sciences, University of Michigan School of Public Health.

Abstracts published in Epidemiology have been reviewed by the organizations of Epidemiology. Affliate Societies at whose meetings the abstracts have been accepted for presentation. These abstracts have not undergone review by the Editorial Board of Epidemiology.


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Infants born prematurely are at higher risk for adverse developmental and health outcomes than infants born at term. Although the causes of prematurity are not definitively known, environmental exposures such as air pollution, in addition to individual clinical, behavioral, and socio-economic factors, may contribute to this outcome and present an important opportunity for preventive interventions.

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We examined the associations between exposures to outdoor air pollutants, including particulate matter less than ten microns in aerodynamic diameter (PM10), ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and preterm birth in Mexico City.

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Data from mother-infant pairs enrolled in the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) study from 1992–2002 were analyzed. Women were excluded from the study if they lacked complete information on the following covariates: mother’s age, years of education, marital status, smoking status during pregnancy (yes or no), parity, calf circumference, or previous adverse birth outcomes (defined as any previous stillborn, miscarried, preterm, or low birth weight infants). Daily pollutant averages from the metropolitan Mexico City air quality monitoring network were used to assign trimester-specific and full pregnancy exposure levels to the 807 women who met the study inclusion criteria. Of these women, 53 (6.6%) delivered preterm. We used a logistic regression model to evaluate the effect of an interquartile range increase in the estimated exposure on the likelihood of preterm birth, adjusting for potential confounding variables (see covariates listed above).

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Preliminary results demonstrate a significant increased risk in the likelihood of preterm birth associated with O3 exposure over the entire pregnancy (adjusted OR = 2.01; 95%CI = 1.09, 3.71; IQR = 0.01 ppm). We also found associations with PM10 (adjusted OR = 1.49; 95%CI = 0.98, 2.27; IQR = 1.49 μg/m3) and SO2 (adjusted OR = 1.56; 95%CI = 0.96, 2.55; IQR = 0.02 ppm) during the first trimester, which are consistent with previously published studies.

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These preliminary results, which adjust for many individual risk factors, show an association between O3 and increased risk of preterm birth and suggest an effect from PM10 and SO2. The PM10 and SO2 associations we observed are consistent with other birth outcomes literature, while the O3 results are notable in that few other studies have reported associations with this oxidant pollutant, which is found at high levels in Mexico City.

© 2008 Lippincott Williams & Wilkins, Inc.