Endocrine Abstracts

Aim: Our aim was to investigate the frequency of isolated maternal hypothyroxinemia (IMH) at gestational diabetes mellitus (GDM)

Material and method: Fifty women with GDM aged between 20–41 and 100 healthy pregnant aged between 17–41 were involved to study. Patients that have thyroid disease and low free T₄ levels at first trimester were ruled out. Thyroid function tests of patients and healthy controls were assessed at first, second and third trimester with standard reference ranges (SRR) and method specific trimester reference ranges (MSTRR).75 gram glucose tolerance test was performed to all participants at 24–28 week.

Findings: In both patient and control groups 1st trimester fT₄ levels (fT4₁) were inside normal SRR and there was not any statistical significance. Ft₄ levels that measured at 2nd and 3rd trimester(fT4₂ and fT4₃) were under normal reference ranges in GDM group and GDM group had statistically significant low values. When assessed the fT4₂ and fT4₃ with MSTRR, GDM patients had lower levels but both fT4₂ and fT4₃ levels were inside the normal ranges (P<0.05).IMH frequency due to SRR in GDM and control group was 56 and 13% respectively at 2nd trimester, 88 and 44% at 3rd trimester. IMH frequency due to MSTRR in GDM group was 12–36% at 2nd and 3rd trimester respectively, in control group there was not any IMH at 2nd trimester and 1% at 3rd trimester.

Conclusion: Overt, subclinical maternal hypothyroidism is associated with significant adverse events to both mother and fetus. But knowledge about IMH is limited. It is not clearly known whether IMH is a physiologic change or a marker of a subclinical thyroid disease. Thyroid hormones have a role in regulation of insulin secretion. The relationship between thyroid hormones and diabetes was revealed in many studies. Furthermore few studies showed that hypothyroidism increases the insulin resistance. Due to increase in IMH frequency in our study, our results suggest that IMH may be associated with insulin resistance as seen in overt and subclinical hypothyroidism.