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Jun Wu,^1,2 Cizao Ren,² Ralph J. Delfino,² Judith Chung,³ Michelle Wilhelm,⁴ and Beate Ritz⁴

¹Program in Public Health, College of Health Sciences, and ²Department of Epidemiology, and ³Department of Obstetrics and Gynecology, School of Medicine, University of California, Irvine, California, USA; ⁴Department of Epidemiology, School of Public Health, University of California, Los Angeles, California, USA

Abstract
Background: Preeclampsia is a major complication of pregnancy that can lead to substantial maternal and perinatal morbidity, mortality, and preterm birth. Increasing evidence suggests that air pollution adversely affects pregnancy outcomes. Yet few studies have examined how local traffic-generated emissions affect preeclampsia in addition to preterm birth.

Objectives: We examined effects of residential exposure to local traffic-generated air pollution on preeclampsia and preterm delivery (PTD) .

Methods: We identified 81,186 singleton birth records from four hospitals (1997–2006) in Los Angeles and Orange Counties, California (USA) . We used a line-source dispersion model (CALINE4) to estimate individual exposure to local traffic-generated nitrogen oxides (NO_x) and particulate matter < 2.5 µm in aerodynamic diameter (PM_2.5) across the entire pregnancy. We used logistic regression to estimate effects of air pollution exposures on preeclampsia, PTD (gestational age < 37 weeks) , moderate PTD (MPTD ; gestational age < 35 weeks) , and very PTD (VPTD ; gestational age < 30 weeks) .

Results: We observed elevated risks for preeclampsia and preterm birth from maternal exposure to local traffic-generated NO_x and PM_2.5. The risk of preeclampsia increased 33% [odds ratio (OR) = 1.33 ; 95% confidence interval (CI) , 1.18–1.49] and 42% (OR = 1.42 ; 95% CI, 1.26–1.59) for the highest NO_x and PM_2.5 exposure quartiles, respectively. The risk of VPTD increased 128% (OR = 2.28 ; 95% CI, 2.15–2.42) and 81% (OR = 1.81 ; 95% CI, 1.71–1.92) for women in the highest NO_x and PM_2.5 exposure quartiles, respectively.

Conclusion: Exposure to local traffic-generated air pollution during pregnancy increases the risk of preeclampsia and preterm birth in Southern California women. These results provide further evidence that air pollution is associated with adverse reproductive outcomes.

Key words: air pollution, nitrogen oxides, particulate matter, preeclampsia, pregnancy outcome, preterm birth, vehicle emission. Environ Health Perspect 117:1773–1779 (2009) . doi:10.1289/ehp.0800334 available via http://dx.doi.org/ [Online 23 June 2009]

Address correspondence to J. Wu, Program in Public Health, College of Health Sciences, 100 Theory Dr., Suite 100, University of California, Irvine, CA 92697-7555 USA. Telephone: (949) 824-0548. Fax: (949) 824-1343. E-mail: junwu@uci.edu

Supplemental Material is available online (doi:10.1289/ehp.0800334.S1 via http://dx.doi.org/) .

We thank staff at the Memorial Care Medical Centers for assistance with the project.

The study was supported by the National Institute of Environmental Health Sciences (1R21ES016379-01A1 to J.W. and R01ES010960-01 to B.R.) and a Faculty Research Award from the College of Health Sciences, University of California, Irvine (J.W.) .

The authors declare they have no competing financial interests.

Received 28 October 2008 ; accepted 23 June 2009.