OBJECTIVE: To evaluate the association of maternal serum 25-hydroxyvitamin D 
(25[OH]D) status with glucose homeostasis and obstetric and newborn outcomes in 
women screened for gestational diabetes mellitus (GDM).
METHODS: Consecutive women were screened for GDM at 24 to 28 weeks' gestation 
during the months of maximal sunlight exposure in Spain (June through 
September). Serum 25(OH)D levels and parameters of glucose homeostasis were 
measured. Outcomes of the delivery and newborn were collected.
RESULTS: Two hundred sixty-six women were screened. Vitamin D deficiency 
(25[OH]D <20 ng/mL) was observed in 157 women (59%). We observed an inverse 
correlation between 25(OH)D levels and hemoglobin A1c, homeostasis model 
assessment of insulin resistance, serum insulin, and fasting and 1-hour oral 
glucose tolerance test glucose levels (P<.001). With a 25(OH)D concentration 
less than 20 ng/mL, the odds ratios were 3.31 for premature birth (95% 
confidence interval, 1.52-7.19; P<.002) and 3.93 for cesarean delivery (95% 
confidence interval, 2.00-7.73; P<.001). A 25(OH)D concentration of 20 ng/mL had 
79% sensitivity and 51% specificity for cesarean delivery and 80% sensitivity 
and 45% specificity for premature birth. The cutoffs with the best combination 
of sensitivity and specificity were 16 ng/mL for cesarean delivery (62.9% 
sensitivity and 61.2% specificity) and 14 ng/mL for premature birth (66.7% 
sensitivity and 71.0% specificity).
CONCLUSIONS: In the population we sampled, vitamin D deficiency is very common 
during pregnancy. Lower 25(OH)D levels are associated with disorders of glucose 
homeostasis and adverse obstetric and newborn outcomes.