Frequency of isolated maternal hypothyroxinemia in women with gestational diabetes mellitus in a moderately iodine-deficient area.

AIM: To investigate frequency of isolated maternal hypothyroxinemia (IMH) in women with gestational diabetes mellitus (GDM) using both the method specific trimester range (MSTR) and the standard reference range (SRR).

METHODS: Our study included 50 GDM patients (case group) and 60 non-GDM pregnant (control group). Glucose, insulin, HOMA-IR, fT4 and TSH values were measured when pregnancy was confirmed in all participants. Thyroid function tests were measured in each trimester using the SRR and the MSTR.

RESULTS: In the second and third trimesters, mean fT4 levels were significantly lower in the case group compared to the control group, based on the SRR (p < 0.001). Mean fT4 levels were within the normal reference range in both groups, based on the MSTR; however, the levels were significantly lower in the case group (p < 0.001). Using the SRR, IMH frequencies in the second and third trimesters, in the case group were 56 and 86%, respectively, and were 13.3 and 46.7%, respectively, in the control group (p < 0.001). Using the MSTR, the IMH frequencies in the second and third trimesters were 8 and 14%, respectively; there were no instances of IMH in the control group.

CONCLUSION: This study shows that changes in glucose metabolism may affect the thyroid hormone levels (fT4). Additionally, evaluating thyroid function tests in GDM patients using the MSTR can give more accurate results.