Joint effect of ambient PM2.5 exposure and vitamin B12 during pregnancy on the risk of gestational diabetes mellitus

Evidence has indicated that the risk of gestational diabetes mellitus (GDM) was linked to PM2.5 exposure during pregnancy, but findings on susceptible exposure windows are inconsistent. Further, previous studies have not paid attention to B12 intake in the relationship between PM2.5 exposure and GDM. The study is aimed to identify the strength and exposure periods for associations of PM2.5 exposure with GDM, followed by exploring the potential interplay of gestational B12 levels and PM2.5 exposure on the risk of GDM. The participants were recruited in a birth cohort between 2017 and 2018, and 1396 eligible pregnant women who completed a 75-g oral glucose tolerance test (OGTT) were included. Prenatal PM2.5 concentrations were estimated using an established spatiotemporal model. Logistic and linear regression analyses were used to test associations of gestational PM2.5 exposure with GDM and OGTT-glucose levels, respectively. The joint associations of gestational PM2.5 exposure and B12 level on GDM were examined under crossed exposure combinations of PM2.5 (high versus low) and B12 (insufficient versus sufficient). In the 1396 pregnant women, the median levels of PM2.5 exposure during the 12 weeks before pregnancy, the 1st trimester, and the 2nd trimesters were 59.33 μg/m3, 63.44 μg/m3, and 64.39 μg/m3, respectively. The risk of GDM was significantly associated with a 10 μg/m3 increase of PM2.5 during the 2nd trimester (RR = 1.44, 95 % CI: 1.01, 2.04). The percentage change in fasting glucose was also associated with PM2.5 exposure during the 2nd trimester. A higher risk of GDM was observed among women with high PM2.5 exposure and insufficient B12 levels than those with low PM2.5 and sufficient B12. The study supported higher PM2.5 exposure during the 2nd trimester is significantly associated with GDM risk. It first highlighted insufficient B12 status might enhance adverse effects of air pollution on GDM.