ObjectiveTo evaluate the relationship between vitamin D receptor (VDR) gene polymorphism (FokI[rs10735810]) and serum vitamin D concentration in gestational diabetes mellitus (GDM).MethodsA prospective case-control study that recruited healthy pregnant women (control group) (n =78) and women with GDM (GDM group) (n =79), with no other comorbidities. Peripheral blood samples were collected in the 3rdtrimester of gestation, and all of the pregnant women were followed-up until the end of the pregnancy and the postpartum period. Serum vitamin D concentrations were measured by high-performance liquid chromatography (HPLC). For genomic polymorphism analysis, the genomic DNA was extracted by the dodecyltrimethylammonium bromide/cetyltrimethylammonium bromide (DTAB/CTAB) method, and genotyping was performed by the polymerase chain reaction – restriction fragment length polymorphism (PCR-RFLP) technique, using the restriction enzymeFokI. The Student-t, Mann-Whitney, chi-squared, and Fischer exact tests were used for the analysis of the results.ResultsThere was no significant difference between the pregnant women in the control and GDM groups regarding serum vitamin D levels (17.60 ± 8.89 ng/mL versus 23.60 ± 10.68 ng/mL;p= 0.1). Also, no significant difference was detected between theFokIgenotypic frequency when the 2 groups were compared with each other (p= 0.41).ConclusionThere was no association between theFokIpolymorphism and the development of GDM, nor was there any change in serum vitamin D levels in patients with GDM.