Gestational diabetes mellitus and exposure to ambient air pollution and road traffic noise: A cohort study

Background: Road traffic is a main source of air pollution and noise. Both exposures have been associated with type 2 diabetes, but associations with gestational diabetes mellitus (GDM) have been studied less. Objectives: We aimed to examine single and joint associations of exposure to air pollution and road traffic noise on GDM in a prospective cohort. Methods: We identified GDM cases from self-reports and hospital records, using two different criteria, among 72,745 singleton pregnancies (1997-2002) from the Danish National Birth Cohort. We modeled nitrogen dioxide (NO2) and noise from road traffic (L-den) exposure at all pregnancy addresses. Results: According to the two diagnostic criteria: the Danish clinical guidelines, which was our main outcome, and the WHO standard during recruitment period, a total of 565 and 210 women, respectively, had GDM. For both exposures no risk was evident for the common Danish criterion of GDM. A 10-mu g/m(3) increase in NO2 exposure during first trimester was, however, associated with an increased risk of WHO-GDM (adjusted odds ratio (OR) = 1.24; 95% confidence interval (CI): 1.03, 1.49). The corresponding OR associated with a 10-dB higher road traffic noise level was 1.15 (0.94 to 1.18). In mutually adjusted models the OR for NO2 remained similar 1.22 (0.98, 1.53) whereas that for road traffic noise decreased to 1.03 (0.80, 1.32). Significant associations were also observed for exposure averaged over the 2nd and 3rd trimesters and the full pregnancy. Conclusions: No risk was evident for the common Danish criterion of GDM. NO2 was associated with higher risk for GDM according to the WHO criterion, which might be due to selection bias.