The association between prenatal PM2.5 constituent exposure and gestational diabetes mellitus: Exploratory analysis of the potential modifying role of thyroid hormones

The associations of PM 2.5 constituents with blood glucose and GDM remain unclear, and the interplay between PM 2.5 exposure and thyroid hormone levels in relation to GDM has not been well characterized. This retrospective cohort study included 1314 pregnant women with data collected through multiple methods. A generalized linear model analyzed PM 2.5 -glucose links, logistic regression assessed pollutant-GDM associations, and stratified analyses explored these relationships at different thyroid hormone levels. In the study population, first-trimester exposure to SO 4 2- and BC correlated positively with FBG, as did PM 2.5 and its components in the second trimester. First-trimester SO 4 ²⁻ exposure (OR=1.26, 95% CI: 1.06, 1.51) and second-trimester exposures to PM 2.5 (OR=1.67, 95% CI: 1.19, 2.35), NO 3 ⁻ (OR=1.34, 95% CI: 1.06, 1.68), and NH 4 ⁺ (OR=1.33, 95% CI: 1.06, 1.65) were associated with increased GDM risk. Stratified analyses showed that second-trimester BC and OM were positively correlated with FBG in the high-TSH and low-FT4 strata, respectively. In addition, first-trimester exposure to SO 4 2- (high TSH: OR = 1.42, 95% CI: 1.10, 1.84; low FT4: OR = 1.35, 95% CI: 1.05, 1.74) and to PM 2.5 (high TSH: OR = 1.93, 95% CI: 1.14, 3.27; low FT4: OR = 1.82, 95% CI: 1.46, 2.25) in the second trimester were associated with higher odds of GDM. These findings show that PM 2.5 exposure was associated with glucose dysregulation and GDM in pregnant women differently by trimester and component. Across the separate TSH- and FT4-stratified analyses, women in the high-TSH and low-FT4 strata, respectively, appeared to show greater susceptibility to air pollution-related GDM. These subgroup findings should therefore be interpreted as exploratory and require validation in future studies.