Association of Vitamin D and Parathyroid Hormone with Insulin Sensitivity, Beta Cell Function and Gestational Diabetes in Pregnancy: A Cross-Sectional, Observational Study

Vitamin D (25OHD) and parathyroid hormone (PTH) are associated with dysglycemia, and we investigated them in gestational diabetes mellitus (GDM). In this cross-sectional, observational study, we included 75 pregnant women between 24 and 28 weeks of gestation. A fasting venous sample was collected for plasma glucose (FPG), insulin, PTH and 25OHD. Glucose and insulin samples were collected hourly after 75 g glucose load for 2 h. Insulin sensitivity was estimated by the Matsuda index (MI) and beta cell function by the insulin secretion sensitivity index (ISSI-2). The subjects were stratified into three groups and tertiles according to the 25OHD and PTH, respectively. Appropriate statistical tests were used to compare the MI, ISSI-2 and GDM among the groups. GDM was seen in 14/75, and of these patients, 2 were 25OHD deficient, 7 insufficient and 5 had sufficient 25OHD. MI and ISSI-2, though not correlated with the 25OHD, decreased from the lower to higher PTH tertile (P < 0.001). FPG, AUCgluc (area under the curve glucose) and prevalence of GDM increased from the lower to higher PTH tertile (P < 0.001). Increased PTH was associated with decreased insulin sensitivity, beta cell function and GDM in pregnancy, irrespective of the underlying 25OHD level.