Early Pregnancy Maternal Vitamin D Concentrations and Risk of Gestational Diabetes Mellitus

Background While associations of vitamin D deficiency with type 2 diabetes have been well demonstrated, investigations of vitamin D and risk of gestational diabetes mellitus ( GDM ) reported inconsistent findings. We examined associations of vitamin D status with GDM . Methods In a nested case‐cohort study (135 GDM cases and 517 non‐ GDM controls), we measured maternal serum vitamin D status (total 25[ OH ] D and 25[ OH ] D 3 ) in early pregnancy (16 weeks on average) using liquid chromatography‐tandem mass spectroscopy. GDM was diagnosed according to the A merican D iabetes A ssociation guidelines. We calculated adjusted odds ratios and 95% confidence intervals ( CI s) using logistic regression models. Results GDM cases had lower mean total 25[ OH ] D (27.3 vs. 29.3 ng/m L ) and 25[ OH ] D 3 (23.9 vs. 26.7 ng/m L ) concentrations compared with women who did not develop GDM (both P ‐values < 0.05). Overall, 25[ OH ] D 3 concentrations, but not total 25[ OH ] D concentrations, were significantly associated with GDM risk. A 5‐ng/m L increase in 25[ OH ] D 3 concentration was associated with a 14% decrease in GDM risk ( P ‐value = 0.02). Women in the lowest quartile for 25[ OH ]D 3 concentration had a twofold [95% CI 1.15, 3.58] higher risk of GDM compared with women in the highest quartile ( P ‐value for trend < 0.05). Conclusions Early pregnancy vitamin D status, particularly 25[ OH ] D 3 , is inversely associated with GDM risk.