Association of Vitamin D and Glucose Tolerance and Adverse Pregnancy Outcomes in Pregnant Women

Background and Objective: Vitamin D is linked to glucose metabolism, but its role in gestational diabetes is unclear. This study seeks to determine the effect of vitamin D status on glucose tolerance test results and adverse pregnancy outcomes in pregnant women. Methods: A post hoc analysis of two vitamin D supplementation studies with a total of 546 pregnant women was conducted. Vitamin D status (25(OH)D) was determined by radioimmunoassay. Serum glucose concentrations were evaluated by a 2-step diagnostic screening for gestational diabetes with a cutoff for an abnormal 1-hour screen of 139 mg/dL and 2 abnormal values on a 3-hour oral glucose tolerance test. Adverse outcomes analyzed were preterm birth (<37 weeks), birth weight <1500 grams, macrosomia/large for gestational age (LGA), need for NICU admission, and non-repeat Caesarian section. Results: Vitamin D deficiency (<20 ng/mL or 50nmol/L) and insufficiency (<30 ng/mL or 75 nmol/L) were associated with glucose tolerance test results >139 mg/dL when controlling for BMI >30 and ethnicity (p<0.0001). A screening glucose tolerance test result of >139 mg/dL was also significantly associated with non-repeat Cesarean section deliveries (p=0.0308). Discussion: Vitamin D deficiency and insufficiency were associated with an increased risk of failing a screening glucose tolerance test during pregnancy, suggesting that vitamin D deficiency is a risk factor for glucose intolerance and potentially gestational diabetes.