[Subclinical hypothyroidism and pregnancy]

Pregnancy has an important impact on thyroid homeostasis. The main hormonal criteria of the thyroid function are modified particularly in case of low iodine supply. Subclinical hypothyroidism is defined by a slight elevation of TSH (with a cut-off still under discussion near to 4 mU/l) although serum thyroxine and triiodothyronine levels are within the normal range. Maternal morbidity as well as prenatal morbidity and consequences on the neuropsychological development of the child are fairly well established in subclinical hypothyroidism. However, to date, there are no convincing trials assessing the efficacy levothyroxine in subclinical hypothyroidism all the more when TSH levels are between 3 and 4 mU/l. Therefore routine screening for and treatment of subclinical hypothyroidism during pregnancy are unwarranted.