Isolated Maternal Hypothyroxinemia May be Associated with Insulin Requirement in Gestational Diabetes Mellitus.

An insulin regimen may be necessary for about 30% of the patients with gestational diabetes mellitus (GDM). We aimed to investigate the association of free T4(fT4) levels with insulin requirement in pregnant women with GDM. We included pregnant women whose TSH levels were within the normal range and who were diagnosed with GDM, and excluded patients with thyroid dysfunction, chronic illnesses, or any previous history of antithyroid medication, levothyroxine, or antidiabetic medication use. The diagnosis and treatment of GDM were based on American Diabetes Association guidelines. Demographic features, previous history of GDM and gestational hypertension were recorded. Baseline (at diagnosis of GDM) fasting blood glucose, HbA1c, TSH, fT4, and fT3 levels were analyzed. We grouped the patients according to their baseline fT4 levels: isolated maternal hypothyroxinemia (IMH) (group A) vs. in the normal range (group B). We grouped those also based on insulin requirement in 3rd trimester. Of the patients (n=223), insulin requirement was present in 56, and IMH in 11. Insulin requirement was more frequent in group A than in group B (p=0,003). HbA1c (≥47,5 mmol/mol) and fT4 level (lower than normal range) were positive predictors for insulin requirement (OR:35,35, p=0,001; and OR:6,05, p=0,008; respectively). We showed that IMH was closely associated with insulin requirement in GDM. Pregnant women with IMH and GDM should be closely observed as regards to glycemic control. If supported by future large studies, levothyroxine treatment might be questioned as an indication for patients with GDM and IMH.