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Michelle L. Bell,¹ Keita Ebisu,² and Kathleen Belanger³

¹School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, USA; ²Department of Biostatistics, and ³Department of Epidemiology and Public Health, School of Medicine, Yale University, New Haven, Connecticut, USA

Abstract
Background: Several studies have examined whether air pollution affects birth weight ; however results vary and many studies were focused on Southern California or were conducted outside of the United States.

Objectives: We investigated maternal exposure to particulate matter with aerodynamic diameter < 10, < 2.5 µm (PM₁₀, PM_2.5) , sulfur dioxide, nitrogen dioxide, and carbon monoxide and birth weight for 358,504 births in Massachusetts and Connecticut from 1999 to 2002.

Methods: Analysis included logistic models for low birth weight (< 2,500 g) and linear models with birth weight as a continuous variable. Exposure was assigned as the average county-level concentration over gestation and each trimester based on mother's residence. We adjusted for gestational length, prenatal care, type of delivery, child's sex, birth order, weather, year, and mother's race, education, marital status, age, and tobacco use.

Results: An interquartile increase in gestational exposure to NO₂, CO, PM₁₀, and PM_2.5 lowered birth weight by 8.9 g [95% confidence interval (CI) , 7.0–10.8], 16.2 g (95% CI, 12.6–19.7) , 8.2 g (95% CI, 5.3–11.1) , and 14.7 g (95% CI, 12.3–17.1) , respectively. Lower birth weight was associated with exposure in the third trimester for PM₁₀, the first and third trimesters for CO, the first trimester for NO₂ and SO₂, and the second and third trimesters for PM_2.5. Effect estimates for PM_2.5 were higher for infants of black mothers than those of white mothers.

Conclusions: Results indicate that exposure to air pollution, even at low levels, may increase risk of low birth weight, particularly for some segments of the population.

Key words: Air pollution, birth weight, carbon monoxide, nitrogen dioxide, particulate matter, PM₁₀, PM_2.5, pregnancy, sulfur dioxide. Environ Health Perspect 115:1118–1125 (2007) . doi:10.1289/ehp.9759 available via http://dx.doi.org/ [Online 11 April 2007]

Address correspondence to M.L. Bell, Yale University, School of Forestry and Environmental Studies, 205 Prospect St., New Haven, CT 06511 USA. Telephone: (203) 432-9869. Fax: (203) 432-3817. E-mail: michelle.bell@yale.edu

Supplemental Material is available online at http://www.ehponline.org/docs/2007/9759/suppl.pdf

Funding for M.L.B. and K.E. was provided by the Health Effects Institute through the Walter A. Rosenblith New Investigator Award (4720-RFA04-2/04-16. Funding for M.L.B. was also provided by the National Institute of Environmental Health Sciences (NIEHS) Outstanding New Environmental Scientist (ONES) Award (R01 ES015028) . Funding for K.B. was provided by the Health Effects Institute 4720-FRA04 and by NIEHS grants ES015028, ES07456-07, and ES11013.

The authors declare they have no competing financial interests.

Received 24 September 2006 ; accepted 11 April 2007.