BACKGROUND: The serum level of 25-hydroxyvitamin D deficiency has long been 
suspected as a risk factor for glucose intolerance and perhaps 
1,25-dihydroxyvitamin D has a role in the regulation of insulin secretion. This 
study investigates the relation between 25-hydroxyvitamin D concentrations and 
insulin resistance in pregnant women.
METHODS: A cross-sectional study was conducted on 741 pregnant women referred to 
five educating hospital clinics. Universal screening was performed with a GCT-50 
g, and those with plasma glucose levels > pr = 7.2 mmol/L were diagnosed as GDM 
if they had an impaired GTT-100 g based on Carpenter and Coustan criteria. The 
levels of insulin and C-peptide were measured during OGTT-100 g test. The 
homeostasis model assessment index (HOMA) equation was used as the insulin 
resistance index. The concentrations of 25-hydroxyvitamin D, and PTH were also 
measured.
RESULTS: Total prevalence of vitamin D deficiency (<25 nmol/L) was found in 
70.6% of pregnant women. Prevalence of severe vitamin D deficiency (<12.5) in 
GDM patients was higher than in normoglycaemic pregnancies. The regression model 
revealed a strong correlation between the HOMA index and serum levels of vitamin 
D.
CONCLUSIONS: These results show that a positive correlation of 25(OH) vitamin D 
concentrations with insulin sensitivity and vitamin D deficiency could be a 
confirmative sign of insulin resistance.