BACKGROUND: Vitamin D deficiency has long been suspected as a risk factor for glucose intolerance. This study compared serum levels of 25-hydroxy vitamin D(3) in pregnant women with gestational diabetes mellitus (GDM), impaired glucose tolerance (IGT), and non-GDM control subjects.

METHODS: In this case-control study, 54 women with diagnosed GDM and 39 women with IGT (1 abnormal oral glucose tolerance test) were compared with 111 non-GDM control women in whom GDM were excluded by glucose challenge test. Controls were matched in gestational age, age, and body mass index with IGT and GDM groups.

RESULTS: Maternal serum 25-hydroxy vitamin D(3) concentration in GDM and IGT groups at 24-28 weeks of gestation were significantly lower than non-GDM controls (P = .001). A total of 83.3% of GDM compared with 71.2% of the control group had plasma 25-hydroxy vitamin D(3) concentrations consistent with a diagnosis of vitamin D deficiency (<20 ng/mL; P = .03). Women with GDM had a 2.66-fold increased risk of deficient status (25-hydroxy vitamin D(3) <15 ng/mL) compared with control group.

CONCLUSIONS: These results suggested that rates of vitamin D deficiency are higher among women with IGT/GDM, and the relationship between vitamin D status and glucose tolerance in pregnancy needs further study.