The Impact of the First Trimester and Second Trimester Temperature, Air Pollutants, and Seasonal Variations on the Risk of Gestational Diabetes Mellitus in Twin Pregnancies

<b>Background:</b> Recent studies have primarily focused on the impact of environmental factors on gestational diabetes mellitus (GDM) in singleton pregnancies, with limited research on their effects in twin pregnancies. This study investigates how seasonal variations and environmental exposures impact GDM incidence and its subtypes in twin pregnancies, a high-risk group. <b>Methods:</b> In this retrospective analysis of 3769 twin pregnancies, we categorized recruited participants into GDM and non-GDM groups. We examined the effect of the screening season on oral glucose tolerance test (OGTT) glucose values and the incidence of GDM and its subtypes. Multivariable logistic regressions adjusted for confounders assessed the impact of first and second trimester temperatures and air pollutants on GDM risk. Interaction terms evaluated the combined effects of environmental factors on GDM incidence. <b>Results:</b> Seasonal changes significantly influenced GDM risk, with summer presenting the highest risk (<i>p</i> < 0.05). The first trimester's cooler temperatures were inversely related to GDM; <i>T</i> _mean was significantly and negatively associated with 1-h PG and AUC for glucose, with adjusted <i>β</i> (95% CI) of -0.009 (-0.017, -0.001) and -0.719 (-1.406, -0.031), respectively. While warmer second trimester temperatures increased the risk, <i>T</i> _mean was positively associated with FBG, 1-h PG, 2-h PG, and AUC for glucose, with adjusted <i>β</i> (95% CI) of 0.003 (0.001, 0.005), 0.018 (0.009, 0.026), 0.019 (0.011, 0.027), and 1.723 (0.998, 2.448), respectively. Air pollutant exposure showed varying correlations with GDM risk, with ozone (O₃) levels consistently posing a risk. Higher O₃ exposure in the first and second trimesters was associated with increased odds of GDM, with OR (95% CI) of 1.057 (1.004, 1.112) and 1.052 (1.011, 1.096), respectively. Interaction analysis indicated that certain environmental conditions in the first trimester could reduce GDM risk, while others, particularly involving O₃, increased it. <b>Conclusion:</b> Environmental temperatures and air pollutants, especially O₃, are associated with GDM risk in twin pregnancies, with differing effects between trimesters. These findings suggest that environmental factors should be considered in GDM screening and prevention strategies for twin pregnancies. Further research is needed to understand the underlying mechanisms and to develop trimester-specific interventions.