Endocrine Abstracts (2009) 20 S26.2

Thyroid dysfunction during pregnancy

Malgorzata Karbownik-Lewinska

Department of Oncological Endocrinology, Medical University, Lodz, Poland.

Thyroid physiology demonstrates certain specificity during pregnancy. Due to the increased thyroid hormone formation, observed in the course of gestation, the requirements for dietary iodine increase substantially – according to the current recommendations – to 250 μg/day (but <500 μg/day). Therefore, additional iodine supplementation is advised at the level of 150 μg/day to be administered to every pregnant (and lactating) woman. Thyroid hyperstimulation, caused by human chorionic gonadotrophin (hCG) in the first trimester, is another physiological change during pregnancy, assuming relatively frequently the form of gestational transient thyrotoxicosis which, however, usually needs no treatment. Concerning thyroid pathologies in pregnant women, thyroid dysfunctions, i.e. hyper- and hypothyroidism, occur most frequently in developed countries, both being predominantly of autoimmune etiology. Thus, hyperthyroidism in pregnancy is usually associated with Graves’ disease, whereas hypothyroidism – with Hashimoto’s thyroiditis. The diagnosis is based on abnormal values of thyroid hormones and thyrotropin concentrations, with some difficulties in the interpretation of results occurring in the first trimester, while thyroid antibodies should always be measured. Medical treatment in hyperthyroid pregnant women is the management of choice, with propylthiouracil being the preferred antithyroid drug, although thiamazole is also recommended by some authors as a safe and even more effective agent. Careful control of maternal thyroid function is required during antithyroid drug treatment to avoid fetal hypothyroidism. Replacement therapy with levothyroxine is the treatment of choice in hypothyroidism. Patients with pre-existing hypothyroidism generally require increased thyroxine doses during pregnancy. Subclinical hypothyroidism during pregnancy definitively requires thyroxine treatment. Summing up, appropriate management of thyroid dysfunction in pregnancy ensures excellent maternal and fetal outcomes.

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