Associations of gestational diabetes mellitus with residential air pollution exposure in a large Southern California pregnancy cohort

Background: Studies of effects of air pollution on gestational diabetes mellitus (GDM) have not been consistent, and there has been little investigation of effects of exposure preceding pregnancy. In previous studies, the temporal relationship between exposure and GDM onset has been difficult to establish.

Methods: Data were obtained for 239,574 pregnancies between 1999 and 2009 in a population-based health care system with comprehensive electronic medical records. Concentrations of ambient nitrogen dioxide (NO₂), particulate matter (PM) ≤2.5 μm in aerodynamic diameter (PM_2.5) and ≤10 μm (PM₁₀), and ozone (O₃) during preconception and the first trimester of pregnancy at the residential birth address were estimated from regulatory air monitoring stations. Odds ratios (ORs) of GDM diagnosed in the second and third trimesters in association with pollutant exposure were estimated using generalized estimating equation models adjusted for birth year, medical center service areas, maternal age, race/ethnicity, education, census-tract household income, and parity.

Results: In single-pollutant models, preconception NO₂ was associated with increased risk of GDM (OR = 1.10 per 10.4 ppb, 95% confidence interval [CI]: 1.07, 1.13). First trimester NO₂ was weakly associated with GDM, and this was not statistically significant (OR = 1.02 per 10.4 ppb, 95% CI: 0.99, 1.05). Preconception NO₂ associations were robust in multi-pollutant models adjusted for first trimester NO₂ with another co-pollutant from both exposure windows. In single-pollutant models, preconception PM_2.5 and PM₁₀ associations were associated with increased risk of GDM (OR = 1.04 per 6.5 μg/m³, 95% CI: 1.01, 1.06; OR = 1.03 per 16.1 μg/m³, 95% CI: 1.00, 1.06, respectively), but these effect estimates were not robust to adjustment for other pollutants. In single-pollutant models, preconception and first trimester O₃ were associated with reduced risk of GDM (OR = 0.94 per 15.7 ppb, 95% CI: 0.92, 0.95; OR = 0.95 per 15.7 ppb, 95% CI: 0.94, 0.97), associations that were robust to adjustment for co-pollutants.

Conclusions: Maternal exposure to NO₂ during the preconception trimester may increase risk of GDM.