Vitamin D and parathyroid hormone status in pregnancy: effect on insulin sensitivity, β-cell function, and...

Previous studies have yielded conflicting findings on the relationship between vitamin D deficiency/insufficiency and gestational diabetes mellitus (GDM). We hypothesized that PTH may be an underlying factor relevant to this potential association.

This study sought to evaluate the effect of vitamin D and PTH status on insulin sensitivity, β-cell function, and glycemia in pregnancy.

Five-hundred-twenty-four women underwent a glucose challenge test (GCT) and oral glucose tolerance test (OGTT) in late second/early third trimester. The GCT/OGTT identified 142 women with GDM, 94 with gestational impaired glucose tolerance, 163 with an abnormal GCT and normal OGTT, and 125 with normal GCT and OGTT.

Glycemia was assessed by glucose tolerance status and area under the glucose curve (AUC(gluc)) on the OGTT. Insulin sensitivity and β-cell function were assessed by Matsuda index and Insulin Secretion-Sensitivity Index-2 (ISSI-2), respectively.

There were 166 women (31.7%) with vitamin D deficiency (25-OH-D < 50 nmol/L), 178 (34%) with insufficiency (25-OH-D ≥ 50 nmol/L and < 75 nmol/L), and 180 (34.3%) with sufficiency (25-OH-D ≥ 75 nmol/L). Vitamin D status was not associated with Matsuda index, ISSI-2, AUC(gluc), or glucose tolerance status. In contrast, ISSI-2 decreased and AUC(gluc) increased across ascending tertiles of PTH (P = .06 and P = .002, respectively). Indeed, the prevalence of GDM progressively increased from the first (22.6%) to second (25.8%) to third (33.5%) tertile of PTH (P < .001). On logistic regression analyses, the third tertile of PTH was independently associated with GDM (adjusted OR = 1.82; 95% CI, 1.09-3.02; P = .022), whereas vitamin D deficiency and insufficiency were not significant predictors of GDM.

Increased PTH, rather than vitamin D deficiency/insufficiency, is independently associated with dysglycemia in pregnancy.