Association Between Serum Vitamin D, Insulin Resistance (HOMA-IR), and Gestational Diabetes Mellitus

Aim. To investigate whether early pregnancy serum vitamin D levels and insulin resistance (HOMA-IR) are associated with the development of gestational diabetes mellitus (GDM).

Materials and methods. This prospective cohort study was conducted between 2023 and 2025 and included 850 pregnant women enrolled during early gestation. Baseline serum Vitamin D concentrations were measured. Fasting plasma glucose and fasting insulin were determined, and HOMA-IR was calculated. Participants were followed until 24–28 weeks of gestation, when GDM was diagnosed using a standardized 75 g oral glucose tolerance test. Correlation analysis and multivariate logistic regression were performed to determine associations and predictive relationships.

Results. Women who developed GDM had significantly higher pre-pregnancy BMI (M = 29.8, SD = 5.1) compared to non-GDM women (M = 26.4, SD = 4.7), t(848) = 7.5, p < .001. Similarly, HOMA-IR was significantly elevated in the GDM group (M = 4.3, SD = 1.5) compared to the non-GDM group (M = 3.1, SD = 1.1), t(848) = 9.8, p <0.001. Fasting plasma glucose and fasting insulin were also higher among women with GDM (glucose: M = 5.2, SD = 0.5 vs. M = 4.9, SD = 0.4, t(848) = 5.8, p < .001; insulin: M = 18.5, SD = 5.6 vs. M = 14.3, SD = 4.8, t(848) = 9.2, p < 0.001). There were no statistically significant differences in maternal age (t(848) = 1.8, p = 0.07) or serum vitamin D levels (M = 23.6, SD = 7.2 vs. M = 24.1, SD = 6.8, t(848) = 0.9, p = 0.36) between the groups.

Conclusions. The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) was independently associated with increased risk of gestational diabetes mellitus, while serum vitamin D levels showed no significant relationship, and HOMA-IR demonstrated excellent predictive accuracy for GDM.