Association Between First-Trimester Vitamin D Levels and Gestational Diabetes Mellitus: A Prospective Observational Study From South India.

BACKGROUND: Vitamin D deficiency and gestational diabetes mellitus (GDM) are two overlapping public health concerns that are increasingly prevalent among pregnant women. This study was designed to assess whether serum vitamin D deficiency in the first trimester is associated with the development of GDM in an Indian antenatal population. This study aimed to evaluate the association between first-trimester serum 25-hydroxyvitamin D [25(OH)D] levels and subsequent development of GDM. METHODS: This prospective observational study was conducted over 18 months in a tertiary care center in South India. Eighty-seven singleton pregnant women in their first trimester (<13 weeks of gestation) were recruited. Exclusion criteria included pre-gestational diabetes and a previous history of GDM. Serum 25(OH)D was measured using chemiluminescence immunoassay (CLIA). The oral glucose challenge test was utilized for GDM screening at 24-28 weeks and again at 32-34 weeks. Statistical analyses included logistic regression and an ROC curve to identify predictive thresholds. RESULTS: Vitamin D deficiency (<20 ng/mL) was detected in 60.9% of participants. GDM occurred in 30 women, with a significant association noted between vitamin D deficiency and GDM (p = 0.001). Logistic regression revealed that vitamin D deficiency conferred a fivefold increased risk of GDM (aOR: 5.03; 95% CI: 2.12-11.94). ROC analysis demonstrated high predictive accuracy (AUC = 0.94), with <19.5 ng/mL identified as the optimal threshold (sensitivity: 88.2%, specificity: 91.3%). CONCLUSION: First-trimester vitamin D deficiency was significantly associated with increased risk of developing GDM later in pregnancy. These findings support routine early pregnancy screening for vitamin D and suggest potential benefits of timely nutritional interventions in high-risk populations.