Endocrine Abstracts (2006) 11 P830

Increase of L-thyroxine requirement during pregnancy

L Russo, M Tonacchera, E Gianetti, A Perri, P Vitti & A Pinchera


University of Pisa, Pisa, Italy.


In pregnant women with thyroid diseases an increased amount of LT4 may be required for the correction of hypothyroidism or treatment of nodular goiter. Aim of this study was to assess the amount of the variations of LT4 requirement in pregnant women with thyroid diseases. To address this issue, we retrospectively evaluated a cohort of 107 women treated with LT4 divided in two groups: 42 euthyroid (E) (affected by nodular goiter (NG) treated with LT4 suppressive therapy) and 65 hypothyroid (H). This last group was divided in two subgroups: women with a residual functioning thyroid tissue (R-H) (31 with chronic autoimmune thyroiditis, 14 with post-131-I for Graves’ disease, 1 post-methimazole treatment) and women without residual thyroid tissue (NR-H) (2 thyroid agenesis, 12 post-total thyroidectomy). In E pregnant women the goal was to maintain TSH serum level between 0.1 and 0.4 mU/l, while in H pregnant women the goal was to maintain the TSH serum level between 0.4 and 4.0 mU/l. 16 E and 46 R-H and 14 NR-H pregnant women respected these criteria during the entire pregnancy. Only 3 out of 16 (23%) E had to increase LT4 in order to maintain serum TSH in the appropriate range. The mean increase was 112% at 3rd trimester with respect to pre-gravidic dose. In 34 out of 46 (74%) R-H an increase of L-T4 was necessary to maintain serum TSH in the appropriate range. The mean increase was 142±25% at 3rd trimester with respect to pre-gravidic dose. In 12/14 (86%) NR-H an increase in LT4 dose was required to maintain serum TSH in the appropriate range. The mean increase was 136±42% at 3rd trimester with respect to pre-gravidic dose. In conclusion, a rise in LT4 dose is required in the minority of pregnant women with NG under suppressive therapy. We observed that a rise in LT4 dose is required in the majority of hypothyroid women, especially in those without a residual tissue, in order to maintain TSH serum level in the appropriate range. The increase of LT4 requirement to obtain the appropriate serum TSH levels is higher in hypothyroid with respect to NG pregnant women.

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