Background and objective: According to recent studies, endocrine societies have modified the treatment criteria of subclinical gestational hypothyroidism, increasing TSH upper-limit value commonly set at 2.5 μU/ml to a new threshold set at 4 μU/ml. This change in criteria has responded to numerous studies which seem to indicate that the obstetrical complications do not generally increase despite this variation of the threshold TSH value. A further discussion lays now on whether euthyroid (TSH<4 μU/ml) pregnant women with autoimmune thyroid disease may still benefit from treatment within this 2.54 μU/ml TSH range, as some authors found a higher risk of developing subclinical gestational hypothyroidism in this population. This study aims to evaluate the progression towards subclinical hypothyroidism (TSH≥4 μU/ml) throughout gestation of healthy first-trimester pregnant women with and without positive TPOAb status.
Methods: A prospective observational study was performed, in which TPOAb, TSH and FT4 levels were measured between 8th and 12th weeks of pregnancy from Nov 2017 to Dec 2018 at the screening visit. Later, TSH and FT4 levels were also measured in the third trimester. New hypothyroidism diagnosis in third trimester was recorded, and women were divided in two groups according their TSH value in the first trimester. First group those with TSH<2.5 μU/ml and the second group included those with TSH between 2.5 and 4 μU/ml.
Results: From the 1042 pregnant women who participated in the study, 6.24% (65) were positive for TPOAb. 23 of them were treated with levothyroxine: 13 due to a first-trimester TSH > 4 μU/ml and 10 owing to an abnormal thyroid palpation in women within 2.53.9 μU/ml TSH range. Regarding the group that did not receive treatment (42), 35 showed a TSH<2.5 μU/ml and 7 of them were 2.53.9 μU/ml. None (0%) of the pregnant women from this not-treated group developed a subclinical hypothyroidism (TSH≥4 μU/ml) in the third trimester. In the group of negative thyroid autoimmunity (977), the progression towards subclinical hypothyroidism was of 1.53% (15).
Conclusions: In our population there is no development to hypothyroidism in those women who were not initially treated in the first trimester despite positive TPOAb. The criteria to indicate thyroid hormone was TSH≥4 μU/ml or TSH 2.53.9 μU/ml with abnormal thyroid exploration.
In fact, the incidence of subclinical hypothyroidism in the third trimester was higher in those with negative TPOAb, although it is low (1.53%).
These results require further studies.
18 - 21 May 2019
European Society of Endocrinology