[The Thyroid and Pregnancy].

Pregnancy has a profound impact on the thyroid gland and its function. This has to be considered in the assessment of thyroid function tests on the basis of trimester-specific reference intervals during pregnancy and in the decision making when to start therapy.The adverse impact of overt thyroid disorders in pregnancy is well understood, while the relevance of subclinical thyroid disorders and presence of thyroid antibodies remains a bit controversial. In euthyroid pregnant women with positive thyroid antibodies, levothyroxine (LT4) therapy may be discussed individually in the case of recurrent abortions. Furthermore, the risk of adverse pregnancy outcomes seems to be increased in the presence of both thyroid-stimulating hormone (TSH)-elevation and positive thyroid antibodies. Therefore, in case of subclinical hypothyroidism, taking in consideration the thyroid peroxidase antibody (TPO-Ab)-status individual decision-making and liberal initiation of LT4 therapy is recommended. In contrast, overt hypothyroidism is a strong indication for LT4 administration, aiming at rapid achievement of euthyroidism.The most common cause of hyperthyroidism is transient gestational thyrotoxicosis mediated by human chorionic gonadotropin (hCG), which leads to a reduction or suppression of TSH in the first trimester that does not require antithyroid medication. In other causes of overt hyperthyroidism antithyroid drugs (propylthiouracil or thionamides) need to be considered carefully and require interdisciplinary management.The presented recommendations are based on the current guideline of the American Thyroid Association (ATA) and the European Thyroid Association (ETA) as well as recently published literature.