Treatment of thyroid disease in pregnancy

Five to ten times more prevalent in women than men, thyroid disorders are the most common endocrinopathies of women,(6) affecting 0.2% of all women. Reflecting these statistics, thyroid disorders are also the most common endocrinopathies encountered in pregnancy. Several thyroid disorders are unique to pregnancy; gestational trophoblastic disease or postpartum thyroiditis, for example, may result in acute thyrotoxicosis. Other thyroid endocrinopathies may behave differently during pregnancy; autoimmune thyroid disorders, for example, may become quiescent in pregnancy but may flare in the postpartum period. In both pregnant and nonpregnant women, thyroid hormone is needed to maintain the body's normal metabolic function. Secreted from the gland in a tetra-iodinated form (thyroxine [T-4]), the hormone is deiodinated peripherally to the active form (triiodothyronine [T-3]), which then interacts with nuclear hormone binding sites. These sites regulate the transcription of specific gene products central to the regulation of calorigenesis, oxygen consumption, and other metabolic processes. Not surprisingly, therefore, the thyroid is an important regulator of the unique metabolic demands of a normal pregnancy. In women of reproductive age, either hypo- or hyperthyroidism may result in decreased fertility and increased rates of miscarriage, and, accordingly, there may be significant benefit to diagnosing and controlling thyroid disorders before conception. These advantages aside, many women are first diagnosed in pregnancy, one of the few times when young, healthy women enter the health care system. In pregnancy both over- and under-function of the gland are associated with significant maternal morbidity. Effects of thyroid disease in pregnancy, however, are not limited to mothers, for fetal well being may also be compromised by maternal thyroid dysregulation. In areas of iodine deficiency, for example, maternal hypothyroxinemia may be common and is associated with neonatal hypothyroidism and endemic cretinism (see below). Similarly, treatment of the mother may affect fetal thyroid function. Whenever pregnant women are treated for thyroid disorders, the clinician managing their care must consider the effects of treatment on the fetus and adapt therapy accordingly. In order to manage thyroid dysregulation in pregnancy, it is important first to understand those changes in thyroid anatomy and activity expected in euthyroid pregnancies.