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 al l women. Reflecting these statistics, thyroid disorders are also the m ost common endocrinopathies encountered in pregnancy. Several thyroid disorders are unique to pregnancy; gestational trophoblastic disease o r postpartum thyroiditis, for example, may result in acute thyrotoxico sis. Other thyroid endocrinopathies may behave differently during preg nancy; 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-iodin ated form (thyroxine [T-4]), the hormone is deiodinated peripherally t o 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, t herefore, the thyroid is an important regulator of the unique metaboli c demands of a normal pregnancy. In women of reproductive age, either hypo- or hyperthyroidism may result in decreased fertility and increas ed rates of miscarriage, and, accordingly, there may be significant be nefit to diagnosing and controlling thyroid disorders before conceptio n. 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 a ssociated with significant maternal morbidity. Effects of thyroid dise ase in pregnancy, however, are not limited to mothers, for fetal well being may also be compromised by maternal thyroid dysregulation. In ar eas of iodine deficiency, for example, maternal hypothyroxinemia may b e common and is associated with neonatal hypothyroidism and endemic cr etinism (see below). Similarly, treatment of the mother may affect fet al thyroid function. Whenever pregnant women are treated for thyroid d isorders, the clinician managing their care must consider the effects of treatment on the fetus and adapt therapy accordingly. In order to m anage thyroid dysregulation in pregnancy, it is important first to und erstand those changes in thyroid anatomy and activity expected in euth yroid pregnancies.