Endocrine Abstracts

Objectives: The association between thyroid function variations and body mass index (BMI) has been described in the adult population in several studies: higher TSH values and lower FT4 values, while still within reference range, have been correlated with higher BMI values. The aim of the study was to assess thyroid hormones variations in relation to body weight in pregnant women without thyroid diseases.

Methods: In this prospective study, thyroid function of 601 pregnant consecutive women without thyroid disease was examined based on pre-pregnancy weight and weight gain at the end of the gestation. In particular, 141 women (23.5%) had a pre-pregnancy BMI <20 kg/m2, 335 (55.7%) had a BMI between 20-25 kg/m2, 88 (14.6%) had a BMI between 25-30 kg/m2 and 37 (6.2%) had a BMI >30 kg/m2. The difference in the mean age between normal weight (34 ± 5.18 DS) and obese patients (33 ± 5.87 DS) was not statistically significant. Throughout each trimester, thyroid function (TSH, FT4 and FT3 values), the presence of anti-thyroid antibodies (AbTg and AbTPO), thyroid ultrasound and patients’ anthropometric and hormonal data were assessed.

Results: Comparing thyroid function based on pre-pregnancy BMI, significantly higher TSH values (1.54 mUI/l [1.17 IQR] vs 1 mUI/l [1.02 IQR], P = 0.034) were observed in obese women in the first trimester of pregnancy compared to normal-weight women. Furthermore, women who gained more than 15 kg during pregnancy had significantly lower FT4 levels at the end of pregnancy compared to women who gained less weight. This finding is significant in the overall population of women (0.75 ng/dL [1.83 IQR] vs 0.82 ng/dL [0.17 IQR], P = 0.000) or, when divided by BMI at the beginning of pregnancy, in women who were normal weight in the early first trimester (0.73 ng/dL [0.17 IQR] vs 0.82 ng/dL [0.15 IQR], P = 0.000), while it was not significant in patients who were overweight or obese at the beginning of pregnancy.

Conclusions: In conclusion, higher TSH levels were observed in women with obesity in the first trimester of pregnancy. Lower FT4 levels were highlighted in women with greater weight gain during pregnancy, particularly in patients who were normal weight in the early first trimester.