Prenatal exposure to ambient air pollution has been associated with
preterm birth in several studies. Associations between air pollution and gestational or pre-existing diabetes have been hypothesized but are not well established. We examined the association between air pollution exposure in pregnancy and
gestational diabetes and whether the association between air pollution and
preterm birth is modified by
diabetes (gestational or pre-existing) in a highly polluted area of California. Birth certificates and hospital discharge data from all singleton births from 2000 to 2006 to women living in four counties in the San Joaquin Valley of California were linked to criteria air pollution and traffic density measurements at the geocoded maternal residence.
Air pollutants were dichotomized at the highest quartile and compared to the lower three quartiles. Logistic regression models were adjusted for maternal race-ethnicity, age, education, payment of birth expenses, and
prenatal care. There were consistent inverse associations between exposure to air pollution during the first two trimesters and
gestational diabetes (statistically significant odds ratios (OR) less than 1). When stratified by any
diabetes (gestational or pre-existing), associations between air pollution exposure during pregnancy and categories of
preterm birth (20-27, 28-31, 32-33, 34-36 weeks) were generally similar with few exceptions of exposures to
carbon monoxide (CO) and
particulate matter < 2.5 µm (PM2.5). Those with diabetes and exposure higher levels of CO (in first trimester or entire pregnancy) or PM2.5 (in first trimester) had higher risk of extremely
preterm birth (20-27 weeks) compared with those without diabetes. The associations between traffic-related air pollution and
gestational diabetes were in the unexpected ("protective") direction. Among those with any diabetes, associations were stronger between CO and PM2.5 and extremely
preterm birth.