Residential Proximity to Traffic and Adverse Birth Outcomes in Los Angeles County, California, 1994-1996. (Children's Health)

Article excerpt

We reported previously that increases in ambient air pollution in the Los Angeles basin increased the risk of low weight and premature birth. However, ambient concentrations measured at monitoring stations may not take into account differential exposure to pollutants found in elevated concentrations near heavy-traffic roadways. Therefore, we used an epidemiologic case-control study design to examine whether residential proximity to heavy-traffic roadways influenced the occurrence of low birth weight (LBW) and/or preterm birth in Los Angeles County between 1994 and 1996. We mapped subject home locations at birth and estimated exposure to traffic-related air pollution using a distance-weighted traffic density (DWTD) measure. This measure takes into account residential proximity to and level of traffic on roadways surrounding homes. We calculated odds ratios (ORs) and risk ratios (RRs) for being LBW and/or preterm per quintile of DWTD. The dearest exposure-response pattern was observed for preterm birth, with an RR of 1.08 [95% confidence interval (CI), 1.01-1.15] for infants in the highest DWTD quintile. Although higher risks were observed for LBW infants, exposure-response relations were less consistent. Examining the influence of season, we found elevated risks primarily for women whose third trimester fell during fall/winter months (O[R.sub.term LBW] = 1.39; 95% CI, 1.16-1.67; O[R.sub.preterm and LBW] = 1.24; 95% CI = 1.03-1.48; R[R.sub.all preterm] = 1.15; 95% CI, 1.05-1.26), and exposure-response relations were stronger for all outcomes. This result is consistent with elevated pollution in proximity to sources during more stagnant air conditions present in winter months. Our previous research and these latest results suggest exposure to traffic-related pollutants may be important. Key words: air pollution, epidemiology, low birth weight, preterm birth, traffic density. Environ Health Perspect 111:20-216 (2003). [Online 4 November 2002]

doi: 10.1289/ehp.5688 available via


Epidemiologic studies addressing the relationship between ambient air pollution and fetal development are accumulating worldwide. Studies conducted in China (Wang et al. 1997; Xu et al. 1995), Brazil (Pereira et al. 1998), the Czech Republic (Bobak and Leon 1999; Dejmek et al. 1999; Perera et al. 1999), Mexico (Loomis et al. 1999), Korea (Ha et al. 2001), and the United States (Woodruff et al. 1997) linked ambient air pollution exposure during pregnancy with term low birth weight (LBW), intrauterine growth retardation (IUGR), preterm birth, and perinatal mortality. We recently reported that increases in carbon monoxide, particulate matter < 10 lam in aerodynamic diameter (P[M.sub.10]), and ozone concentrations during vulnerable pregnancy periods increased the risk of term LBW (Ritz and Yu 1999), preterm delivery (Ritz et al. 2000), and certain cardiac malformations, such as ventricular septal defects (Ritz et al. 2002). CO is released directly in motor vehicle exhaust and does not react readily in the atmosphere to form other compounds. Fine (< 2.5 lam) and ultrafine (< 0.1 [micro]m) particles are also released directly in vehicle exhaust but undergo physical and chemical transformations in the atmosphere as they disperse from the roadway (Zhu et al. 2002). The consistently observed associations between ambient CO concentrations and adverse birth outcomes in our previous studies suggest that compounds in motor vehicle exhaust (either CO or associated compounds such as fine and ultrafine particles) may affect fetal development.

In our previous studies (Ritz and Yu 1999; Ritz et al. 2000, 2002), air pollution exposure assessment was based on measurements taken at ambient monitoring stations during specific pregnancy periods. Although such measures may adequately reflect average exposure of pregnant women to background air pollution concentrations in their neighborhood, they may not take into account differential exposure within neighborhoods due to proximity to heavy-traffic roadways and freeways. …