To treat or not to treat euthyroid autoimmune disorder during pregnancy?

Subclinical autoimmune hypothyroidism during pregnancy is associated with an increased risk of miscarriage and has a deleterious effect on fetal development. The aim of this study was to evaluate a screening and treatment strategy of subclinical hypothyroidism, and to establish normal ranges of thyroid-stimulating hormone (TSH) and thyroxine (T(4)) during pregnancy.

A retrospective study was carried out on 784 consecutive files of pregnant women; the files were systematically searched for thyroid function and antithyroid antibodies in order to determine the effect and the prevalence of anti-thyroid peroxidase antibodies (TPO-Ab) during pregnancy, and to evaluate treatment with levothyroxin (LT(4)) in TPO-Ab carriers.

Among the 75 TPO-Ab-positive patients, 42 received LT(4) treatment during pregnancy. Although the range of TSH serum levels was wide, the mean TSH level was significantly higher in TPO-Ab-positive women (3 vs. 1 mIU/l, p < 0.01). No significant difference in the obstetrical complications rate was observed between TPO-Ab-positive and TPO-Ab-negative populations.

Our study provides information on normal ranges of serum TSH and free T(4) for Belgian pregnant women receiving iodide supplementation. Based on our results, we suggest supplementation of TPO-Ab-positive pregnant women with 50 microg/day of LT(4), unless their TSH levels are lower than 1 mIU/l, to avoid the risk of hypothyroidism during pregnancy.