Vitamin D Status during Pregnancy and the Risk of Gestational Diabetes Mellitus: A Longitudinal Study in a Multiracial Cohort

Abstract

Aims Emerging evidence suggests that maternal vitamin D status may be associated with gestational diabetes (GDM). However, the temporal relation remains unclear due to the lack of longitudinal data on vitamin D over pregnancy. We aimed to prospectively and longitudinally investigate vitamin D status during early to mid‐pregnancy in relation to GDM risk. Methods In a nested case‐control study of 107 GDM cases and 214 controls within the Fetal Growth Studies‐Singleton Cohort, plasma levels of 25‐hydroxyvitamin D2 and D3 (25(OH)D) and vitamin D binding protein were measured at gestational weeks 10‐14, 15‐26, 23‐31, and 33‐39; we further calculated total, free, and bioavailable 25(OH)D. Conditional logistic regression models and linear mixed‐effects models were used. Results We observed a threshold effect for the relation of vitamin D biomarkers with GDM risk. Vitamin D deficiency (<50 nmol/L) at 10‐14 gestational weeks was associated with a 2.82‐fold increased risk for GDM [odds ratio (OR) =2.82, 95% confidence interval (CI): 1.15‐6.93]. Women with persistent vitamin D deficiency at 10‐14 and 15‐26 weeks of gestation had a 4.46‐fold elevated risk for GDM compared to women persistently non‐deficient (OR=4.46, 95% CI: 1.15‐17.3). Conclusions Maternal vitamin D deficiency as early as the first trimester of pregnancy was associated with an elevated risk of GDM. The association was stronger for women who were persistently deficient through the 2nd trimester. Assessment of vitamin D status in early pregnancy may be clinically important and valuable for improving risk stratification and developing effective interventions for the primary prevention of GDM.