The relationship between Thyroid dysfunction during pregnancy and Gestational diabetes mellitus.

BACKGROUND: Thyroid dysfunction and gestational diabetes are the two most common endocrine disorders that can be observed during pregnancy. Thyroid function abnormalities could be associated with insulin resistance (IR) and changes in carbohydrate metabolism. In patients with type 1 diabetes, thyroid function is usually evaluated to rule out abnormalities within a second autoimmune disease. Patients with type 2 diabetes are tested for thyroid function in view of the associated weight gain, IR and changes in metabolism. The question arises, should we also look for thyroid dysfunction in patients with gestational diabetes?

AIM: To determine whether there are abnormalities in thyroid hormone levels in pregnant women with gestational diabetes.

MATERIALS AND METHODS: A monocentric, retrospective study of Dr Shterev Hospital electronic database was performed. We analyzed the medical records of 662 pregnant women, divided in two groups- 412 with GDM and 250 with normal glucose tolerance, who gave birth in the period 2017-2019. GDM in the study group was diagnosed using an oral glucose tolerance test. We analyzed the mean serum levels of thyroid stimulating hormone (TSH); free thyroxine levels (FT4), free triiodothyronine levels (FT3), FT3:FT4 ratio, fasting plasma glucose, age and body mass index in both groups. The groups were compared using Mann-Whitney U-test.

RESULTS: In patients who developed GDM significantly higher levels of TSH (p<0.0001) and FT3 (p<0.0001), lower levels of FT4 (p<0.0001) and higher FT3:FT4 ratio (р<0.0001) were found.

CONCLUSION: The results of these pilot retrospective series reveals that high-normal to high levels of TSH and low normal to low levels for FT4 as well as high FT3:Ft4 ratio could indicate increased risk of development of GDM.