Air pollutant exposure and preterm and term small-for-gestational-age births in Detroit, Michigan: Long-term trends and associations

Studies in a number of countries have reported associations between exposure to ambient air pollutants and adverse birth outcomes, including low birth weight, preterm birth (PTB) and, less commonly, small for gestational age (SGA). Despite their growing number, the available studies have significant limitations, e.g., incomplete control of temporal trends in exposure, modest sample sizes, and a lack of information regarding individual risk factors such as smoking. No study has yet examined large numbers of susceptible individuals. We investigated the association between ambient air pollutant concentrations and term SGA and PTB outcomes among 164,905 singleton births in Detroit, Michigan occurring between 1990 and 2001. SO2, CO, NO2, O3 and PM10 exposures were used in single and multiple pollutant logistic regression models to estimate odds ratios (OR) for these outcomes, adjusted for the infant's sex and gestational age, the mother's race, age group, education level, smoking status and prenatal care, birth season, site of residence, and long-term exposure trends. Term SGA was associated with CO levels exceeding 0.75ppm (OR=1.14, 95% confidence interval=1.02–1.27) and NO2 exceeding 6.8ppb (1.11, 1.03–1.21) exposures in the first month, and with PM10 exceeding 35μg/m3 (1.22, 1.03–1.46) and O3 (1.11, 1.02–1.20) exposure in the third trimester. PTB was associated with SO2 (1.07, 1.01–1.14) exposure in the last month, and with (hourly) O3 exceeding 92ppb (1.08, 1.02–1.14) exposure in the first month. Exposure to several air pollutants at modest concentrations was associated with adverse birth outcomes. This study, which included a large Black population, suggests the importance of the early period of pregnancy for associations between term SGA with CO and NO2, and between O3 with PTB; and the late pregnancy period for associations between term SGA and O3 and PM10, and between SO2 with PTB. It also highlights the importance of accounting for individual risk factors such as maternal smoking, maternal race, and long-term trends in air pollutant levels and adverse birth outcomes in evaluating relationships between pollutant exposures and adverse birth outcomes. ► The association between ambient air pollutants and adverse birth outcomes was examined. ► Term small-for-gestational-age (SGA) and preterm birth (PTB) were the main health outcomes. ► Long-term trends in air pollutant levels, and maternal smoking and race were accounted for. ► The early period of pregnancy