Thyroid disease as a teratogen

Maternal thyroid hormones are critical for normal fetal development, particularly brain development. The increase in metabolic demand of pregnancy results in critical physiologic thyroid changes which ultimately lead to an increase in thyroid hormone production. Placental iodothyronine deiodinases tightly regulate the transfer of thyroid hormone to the fetus. As such, too little or excess thyroid hormone can have a teratogenic effect. Therefore, diagnosis and management of thyroid disorders in pregnancy is necessary to prevent adverse maternal, fetal, and neonatal outcomes; however, it remains challenging, in part due to population-, laboratory-, and trimester-specific thyroid hormone reference ranges. Furthermore, certain areas of study remain controversial including whether treatment of subclinical hypothyroidism and isolated thyroid autoimmunity is warranted and consideration of the implementation of universal thyroid screening. This review summarizes the current literature on thyroid physiology and thyroid dysfunction in pregnancy including overt and subclinical hypothyroidism, hyperthyroidism, thyroid autoimmunity, thyroid storm, postpartum thyroiditis, and thyroid cancer.