Ambient air pollution exposure and gestational diabetes mellitus in Guangzhou, China: A prospective cohort study

Evidence concerning the effect of ambient air pollution exposure on gestational diabetes mellitus (GDM) is limited. No published studies have examined maternal weekly air pollution exposure and GDM, and the possible effect modification by folic acid supplementation has not been assessed. To evaluate the association between air pollution exposure and GDM at trimester and weekly levels, and to explore the potential effect modification by folic acid supplementation. A total of 5421 pregnant women were recruited during 2011–2014 in Guangzhou, China. Daily PM2.5, PM10, SO2 and NO2 levels were collected from 10 monitoring stations. Individual's exposure during pregnancy was estimated using inverse-distance weighting approach. Binary logistic regression was used to examine the trimester-specific association between air pollution exposure and GDM. Distributed lag models (DLMs) were applied to estimate maternal weekly air pollution exposure and GDM. Stratified analyses by folic acid supplementation and interaction test were performed. The GDM incidence was 11.69%. An interquartile range (IQR) increase in first trimester SO2 was associated with increased GDM risk in the single pollutant model, the adjusted odds ratio (aOR) and 95% confidence interval (CI) was 1.22 (1.02–1.47). In DLMs, an IQR increase in SO2 during 4th to 10th gestational weeks was associated with increased GDM risk, with the strongest effect in the 7th gestational week. When stratified by maternal folic acid supplementation, first trimester exposure to SO2 was associated with increased GDM risk among women taking folic acid supplements (aOR = 1.25, 95% CI: 1.03–1.53) and P value for interaction was 0.13. No significant effects were observed for PM2.5, PM10 and NO2. First trimester exposure to SO2 was associated with increased GDM risk, especially during the 4th to 10th gestational weeks. The effect might be stronger among women taking folic acid supplements.