Endocrine Abstracts

Objectives: The interplay between thyroid function and metabolic state has been studied in many population subgroups. For pregnant women thyroid and metabolic parameters, including glucose homeostasis, are of great importance for a successful outcome. We examined aspects of thyroid function in relation to GDM and BMI in pregnant women referred to our Department.

Methods: We studied 520 women during 24^th – 32^nd gestation week. Demographic characteristics were recorded and a 75 gr OGTT was performed. Plasma glucose and insulin levels were measured at time 0’-60’-120’. HbA1c and thyroid parameters (TSH, FT4, FT3, FT3/FT4 ratio) were evaluated at time 0’. Thyroid parameters were subjected to multivariate analysis of variance (MANOVA) with the presence of GDM (GDM vs Normal [N]) and BMI (obese (BMI≥30 kg/m²) vs non-obese (BMI<30 kg/m²)).

Results: Of 520 pregnant women, 226 (43.5%) were diagnosed with GDM according to IADSPG/WHO criteria. GDM women were significantly older (33.6±6.2 vs 29.1±6.8 years) and had greater BMI (30.1±5.4 vs 27.7±5.7 kg/m²). TSH levels were lower among non-obese women with GDM versus N (1.8±1.0 vs 2.1±1.2 μUI/ml, P=0.037). FT4 in obese GDM women was lower than in non-obese GDM and obese Normal (11.7±2.3 vs 12.2±1.8 and 12.4±1.5 pmol/l respectively, P=0.03). FT3 levels differed significantly only in the GDM women, between obese and non-obese (4.5±0.6 vs 4.2±0.6 pmol/l, P≤0.001). In accordance, FT3/FT4 ratio was significantly higher in obese GDM women compared to obese Normal and non-obese GDM (0.39±0.07 vs 0.36±0.08 and 0.35±0.06 respectively, P=0.03).

Conclusions: This study shows that (i) GDM is associated with lower TSH levels. (ii) Lower FT4 is associated with both obesity and GDM. (iii) Higher FT3 is associated with obesity in GDM women. (iv) Higher FT3/FT4 ratio is related with the simultaneous presence of GDM and obesity. The pathophysiological mechanisms involved in thyroid hormone metabolism in relation to the presence of GDM and/or obesity need to be further elucidated.