Background: The aim was to investigate the relationship between the vitamin D (VitD) level and the incidence rate of subclinical hypothyroidism in patients with gestational diabetes mellitus (GDM) in early pregnancy.
Methods: Ninety eligible patients who underwent physical examination from March 2015 to September 2017 were selected. The levels of serum 25-hydroxyvitamin D (25-OH-VD), free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH), and thyroid peroxidase antibody (TPOAb) were measured. The correlations of VitD level with those of thyroid function-related indices were analyzed.
Results: The serum 25-OH-VD level was (17.82 ± 3.45) ng/mL in the 90 GDM patients in early pregnancy, including 64.44% patients in VitD deficiency group, 22.22% patients in VitD insufficiency group, and 13.33% in VitD sufficiency group. No significant differences in the levels of serum FT4, FT3, and TSH were found among different VitD groups (p > 0.05), but the level of TPOAb gradually decreased (p < 0.05). There was no significant difference in the incidence rate of subclinical hypothyroidism among different VitD groups (p > 0.05). VitD level was not correlated with those of FT4, FT3, and TSH (p > 0.05), but negatively correlated with that of TPOAb (p < 0.05). An increase of TPOAb level raised the risk of VitD deficiency in pregnant women (p < 0.05). Patients suffered from significant 25-OH-VD deficiency in spring and winter (p < 0.05).
Conclusions: GDM patients in early pregnancy display VitD deficiency, and their serum 25-OH-VD level is affected by seasons and not significantly related to subclinical hypothyroidism. However, the increased level of TPOAb may raise the risk of VitD deficiency in pregnant women.