Research | Children’s Health Residential Exposure to Traffic and Spontaneous Abortion Rochelle S. Green,1 Brian Malig,1 Gayle C. Windham,2 Laura Fenster,2 Bart Ostro,1 and Shanna Swan3 1Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, California, USA; 2Division of Environmental and Occupational Disease Control, California Department of Public Health, Richmond, California, USA; 3Department of Obstetrics and Gynecology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA Background : Studies have shown associations between air pollution or traffic exposure and adverse birth outcomes, such as low birth weight. However, very few studies have examined the effect of traffic emissions on spontaneous abortion (SAB). o Bjectiv : The goal of this study was to determine whether residential exposure to vehicular traffic was associated with SAB. Methods : Pregnant women from a prepaid health plan in California were recruited into a prospec- tive cohort study in 1990–1991. Three measures of traffic exposure were constructed for the 4,979 participants using annual average daily traffic (AADT) counts near each residence and distance from residence to major roads. SAB was examined in relation to the traffic exposure measures using logis- tic regression adjusting for a number of demographic and lifestyle variables. r sulte : Of the traffic measures, maximum annual average traffic within 50 m showed the stron- gest association with SAB, although it was not statistically significant. The adjusted odds ratio (AOR) for the top 90th percentile (AADT greater than 15,199) versus the bottom 75th percentile (AADT = 0–1,089) was 1.18 [95% confidence interval (CI), 0.87–1.60]. However, subgroup analy- ses showed statistically significant associations for traffic with SAB among African Americans (AOR = 3.11; 95% CI, 1.26–7.66) and nonsmokers (AOR = 1.47; 95% CI, 1.07–2.04). c onclusi : In this cohort, living within 50 m of a road with AADT of 15,200 or more was significantly associated with SAB among African Americans and nonsmokers. Further research is needed to confirm these results and possibly elucidate the mechanisms responsible for the findings. k ey words : air pollution, cohort, geographic information system, pregnancy, spontaneous abor- tion, vehicular traffic. Environ Health Perspect 117:1939–1944 (2009). doi:10.1289/ehp.0900943 available via http://dx.doi.org/ [Online 26 August 2009] Air pollution has been strongly associated with a number of adverse health outcomes, ranging from respiratory symptoms to cardio- pulmonary and all-cause mortality (Garshick et al. 2003; Ostro et al. 2006; Pope et al. 2002). Several studies also examined the effects of air pollution on pregnancy, provid- ing evidence that exposure to air pollution is associated with poor birth outcomes, such as low birth weight (Maisonet et al. 2001; Ritz and Yu 1999), small-for-gestational-age (Parker et al. 2005), and preterm birth (Ritz et al. 2000; Xu et al. 1995). These studies are relatively common because they use birth out- come data routinely collected by governmen- tal entities. In contrast, data on spontaneous abortion (SAB) that occurs 20 weeks or ear- lier into gestation are not routinely collected. The literature on the relationship between air pollution and SAB is thus sparse, and the studies have yielded inconclusive results (Hansteen et al. 1996; Hemminki and Niemi 1982). Environmental tobacco smoke (ETS), an exposure that contains many of the same components as vehicle exhaust, has been asso- ciated with an increased risk of SAB (George et al. 2006; Windham et al. 1999), and it seems reasonable that exposure to traffic pol- lutants could have a similar relationship. The Kaiser Pregnancy Outcomes Study cohort, which represents over 5,000 pregnancies and includes data on many potential confounders, provides a unique opportunity to investigate this hypothesis. We chose to examine the association between SAB and air pollution using residen- tial proximity to traffic as a proxy for indi- vidual exposure to traffic pollutants. This approach has been used in a number of other studies assessing the effects of air pollution on other health outcomes (Garshick et al. 2003; Kim et al. 2004) and has been found to cor- relate with actual measured levels of pollutants at study sites (Gauderman et al. 2005; Zhu et al. 2002). In this study, we evaluated the relationship between SAB and traffic exposure derived from the residence of each participant. Methods Subject recruitment and interview. Details of data collection have been published elsewhere (Swan et al. 1998) and are briefly summa- rized here. Between 1990 and 1991, pregnant women were recruited from three regional sites of Kaiser Permanente health maintenance organization in California when they called to schedule their first prenatal appointment. The Kaiser facilities were located in the fol- lowing areas: the East Bay, an area east of San Francisco including Berkeley and Oakland; Santa Clara County, south of San Francisco; and San Bernardino County, east of Los Angeles. This study complied with all applica- ble requirements of the United States including Environmental Health Perspectives • volume 117 | number 12 | December 2009 obtaining institutional review board approval at the participating Kaiser facilities. To be eli- gible to participate, the pregnant women had to be at least 18 years of age, ≤ 12 weeks into their pregnancy (mean = 8 weeks) and either English or Spanish speaking. Of the 7,881 women initially invited for participation, 5,342 women completed a computer-assisted telephone interview some- time during the first 13 weeks of pregnancy. Participants gave informed consent over the telephone. They provided information on residential, medical, and pregnancy history; demographics; employment status and occu- pational exposures; diet; lifestyle; and other factors. A total of 1,412 refused participation, 558 were determined to be ineligible, 268 were not pregnant upon telephone contact, and 301 women either could not be reached or did not complete their interview. Pregnancy outcomes. Pregnancy out- come information was obtained for 99% of those completing interviews. Outcomes were assessed from computerized hospital admis- sion files, and, for pregnancy losses, abstracted medical records. Gestational age was assessed using each woman’s report of her last men- strual period (LMP) during interview. If that calculation was < 4 or > 45 weeks to outcome, gestational age was reassessed based on addi- tional information. Elective abortions (n = 128), ectopic pregnancies (n = 13), and molar pregnancies (n = 4) were excluded from the analysis. Among the remaining nonlive births, SAB was defined as a pregnancy ending at ≤ 20 completed gestational weeks; pregnan- cies ending after that period were considered stillbirths. Multiple live births (n = 55) were treated as a single pregnancy. There were Address correspondence to R. Green, OEHHA, California EPA, 1515 Clay Street, 16th Floor, Oakland, CA 94612 USA. Telephone: (510) 622-2745. Fax: (510) 622-3210. E-mail: sgreen@oehha.ca.gov We thank K. Waller for geocoding addresses and R. McLaughlin for assigning traffic counts near resi- dences. We also thank R. Slama for helpful discussions concerning the temporal component of the analyses. The original data collection for the Pregnancy Outcomes Study was supported by the State of California. The opinions expressed in this article are solely those of the authors and do not represent the policy or position of the State of California or the California Environmental Protection Agency. The authors declare they have no competing financial interests. Received 4 May 2009; accepted 31 August 2009. 1939