Free T4 level may be associated with insulin requirement in gestational diabetes mellitus

IntroductionGestational diabetes mellitus (GDM) may frequently be overcome bynutrition therapy alone, but insulin regimen may be necessary in about 30% of the patients with GDM. It was known that thyroid hormones wereassociated with glucose metabolism. Therefore, we aimed to investigatethe association of fT4 level with insulin requirement in euthyroid pregnantwomen with GDM.Materials and methodsWe consecutively included euthyroid patients with GDM, and excluded thosewith thyroid dysfunction or any previous history of use of levothyroxineor antithyroid drug. The diagnosis of GDM was based on ADA criteria.Demographic features, previous history of GDM, gestational hypertension,insulin requirement (absent vs present or basal vs intensive regimen) anddose, nutrition and exercise adherence, and HbA1c, TSH, fT4, fT3, 25(OH)vitamin D3 levels were analyzed. We grouped the patients according to fT4levels: lower than mid-normal (group A) vs upper than mid-normal (groupB), or lower than normal range vs in normal range. We assessed the patientsin 3rd trimester after 34th weeks of the pregnancy.ResultsOf total (n = 228), insulin was necessary in 58 patients. Insulin use was morefrequent in the patients with fT4 level lower than normal range than thosewith normal fT4 (P = 0.003, OR:5.69 (95% CI 1.60–20.24)). Number ofinsulin injections was higher in group A than group B (0.022). fT4 level wasnot associated with insulin dose, HbA1c level, previous history of GDM, ordiet adherence.ConclusionLower fT4 level even in normal range may worsely affect glucosemetabolism in euthyroid pregnant women with GDM. Our findings suggestthat euthyroid hypothyroxinemia in pregnancy may be associated withdifficulty in control of hyperglycemia. GDM would be an indication fortreatment with levothyroxine in euthyroid hypothyroxinemia.