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

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.