Endocrine Abstracts

Background: The influence of hyperinsulinemia and insulin resistance on thyroid function is debatable. Insulin, as an anabolic hormone, may also play a role in thyroid hypertrophy and nodular goitre development. Some recent reports focus on the possible interplay between thyroid function and glucose status in pregnancy, including gestational diabetes mellitus.

Aim: The study aimed to assess the relationship between insulin resistance indices and thyroid function in pregnancy.

Material and methods: The study included 1069 pregnant women (median age 29 years, IQR-6 years). Serum TSH, FT4, FT3, and aTPO were measured in each patient. Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) index was assessed based on fasting glucose and insulin concentrations. In each pregnant woman, a thyroid ultrasound was also performed.

Results: The study participants were stratified into three groups based on HOMA-IR. Group 1 included 324 women with HOMA-IR <1; group 2 – 570 women with HOMA-IR between 1 and <2.5, and group 3 – 175 women with HOMA-IR<2.5. Group 1 and 2 differed significantly in TSH (1.66 mIU/l vs. 1.84 mIU/l, P=0.0205), and FT3 concentrations (5.12 mIU/l vs. 4.76 mIU/l, P=0.002). No difference was found in FT4 concentrations (12.91 pmol/l vs. 12.65 pmol/l, P=0.1153). Group 1 and 3 differed significantly in TSH (1.66 mIU/l vs. 1.96 mIU/l, P=0.0023), FT4 (12.91 pmol/l vs. 11.47 pmol/l, P=0.0000), and FT3 concentrations (5.12 pmol/l vs. 4.66 pmol/l, P=0.0000). The significant difference between group 2 and 3 was only found for fT4 concentrations (P=0.000) (P values for difference in TSH and FT3 concentrations were 0.1958 and 0.2593 respectively). The groups did not differ in aTPO concentrations. aTPO-positivity was not related to HOMA-IR values (mean HOMA-IR in aTPO-positive and aTPO-negative women was 1.63 and 1.80 respectively, P=0.32).

Fasting insulin >10 mIU/ml was found in 27.53% of pregnant women (286 out of 1039) with thyroid volume <25 mL, in contrast to 36.67% women (11 out of 30) with thyroid volume<25 mL.

Conclusions: our results indicate that insulin resistance may impact thyroid function in pregnancy independently of thyroid autoimmunity, with higher TSH and lower thyroid free hormone concentrations in pregnant women with higher HOMA-IR indices.