Maternal vitamin D in early pregnancy and the risk for gestational diabetes mellitus
B. Bhowmik1, T. Siddiquee1, A. R. Khan1, G.A. Hitman2, A. K. A. Khan1, A. Hussain1
1Centre of Global Health Research, Diabetic Association of Bangladesh, Dhaka, Bangladesh
2Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Blizard Institute: 4 Newark Street, London E1 2AT, UK
Background: Conflicting results currently exists on the association between vitamin D and glucose metabolism. The role of maternal vitamin D status in gestational diabetes mellitus (GDM) is not clear.
Aim: To observe the association between maternal vitamin D concentrations in early pregnancy and risk for GDM. 
Method: A total of 746 women attended in a randomized controlled trial conducted in 5 different areas of capital Dhaka, Bangladesh. Serum 25-hydroxyvitamin D (25-[OH] D) was measured at 8-14 weeks of pregnancy. All participants underwent oral glucose tolerance test at 24-28 weeks of gestation. GDM was defined following the International Association for Diabetes in Pregnancy Study Group (IADPSG) criteria. Logistic regression analysis was performed to assess the independent association between vitamin D and GDM. 
Results:  In this study, 176 (23.6%) women were diagnosed with GDM at 24-28 weeks of pregnancy. Among women who had developed GDM, maternal serum D concentrations at 8-14 weeks of gestation were significantly lower than women without GDM (54.2 vs. 48.1 ng/ml, P = 0.040).  Incidence of GDM in women with vitamin D deficiency (<30 ng/ml), insufficient (30-74 ng/ml) and sufficient (≥75 ng/ml) were 31.5%, 22.0% and 19.0 % respectively (P for trend = 0.022). After the adjustment for maternal age and pre-pregnancy BMI, vitamin D deficiency was associated with an increased risk of 1.80 fold (95% CI: 1.01, 3.22) for GDM. In addition, the risk of GDM increased to 3.28 fold (95% CI: 1.89, 5.73) in women who were both overweight (≥23 Kg/m2) and vitamin D deficient (<30 ng/ml). 
Discussion: Maternal vitamin D deficiency in early pregnancy is significantly associated with an elevated risk for GDM. The risk was higher in women who were both overweight and vitamin D deficient.