Abstract
Thyroid dysfunction during pregnancy can result in serious complications for both the mother and infant. However, these complications can be prevented by the optimal treatment of overt maternal thyroid dysfunction. The serum thyroid-stimulating hormone (TSH) concentration is the most reliable measure of thyroid function during pregnancy. Due to the physiologic changes in TSH levels during pregnancy, the correct interpretation of thyroid function requires knowledge of the gestational week and the appropriate population-based reference interval. In addition to a TSH test, the measurement of thyroid peroxidase antibody helps determine whether to treat subclinical hypothyroidism during pregnancy. Since the use of antithyroid drugs during pregnancy is associated with birth defects, it is recommended to discontinue the medication and to perform repeated thyroid function testing during the first trimester. If therapy is needed during the first trimester, propylthiouracil is preferred over methimazole.
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