Association between ambient air pollution and birth weight in southern Nevada

An association between outdoor air pollution and adverse pregnancy outcomes has been reported in recent studies. The aim of this study is to explore the relation between maternal exposure to air pollution and infant health in Southern Nevada.

The frequency of low birth weight (LBW) was assessed from a retrospective cohort of singletons born in Clark County during the period 1995-2008. For each individual birth, information on gestational age, type of delivery, birth weight, sex, maternal age, maternal education, maternal race, marital status, parity, adequacy of prenatal care, and maternal tobacco and alcohol use was available from the state birth registry. Overall, the study cohort consisted of 214,076 singleton children having complete data on birth outcome covariates, excluding those weighing below 1,000 or above 5,500 grams at birth, those born before 37 or after 42 weeks of gestation, and those whose mothers suffered from hypertension, diabetes, or uterine bleeding during pregnancy. Daily air monitoring data was obtained from the U.S. Environmental Protection Agency to estimate average trimester exposures to ambient air pollutants for which routine sampling was conducted during the period 1994-2008. The effects of ambient pollution exposure on LBW were estimated by logistic regression with adjustment for co-risk factors, period of birth and seasonality.

Within the study cohort of live term births, 4,710 (2.2%) were low in birth weight (below 2,500 g). Adjusting for individual covariates and average pollutant measurements in each trimester (trimester exposures assessed simultaneously), exposure to ambient CO during the third trimester was associated with a significantly increased risk for LBW (odds ratio per 1-ppm increment=1.25, 95% confidence interval, 1.06-1.47). There was no indication of a robust association between term LBW and prenatal exposures to other criteria pollutants where measurement data were available.