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.