The most common thyroid abnormalities in women, autoimmune thyroid disorders, represent the combined effects of the multiple thyroid autoantibodies (365). The various antigen–antibody reactions result in the wide clinical spectrum of these disorders. Transplacental transmission of some of these immunoglobulins may affect thyroid function in the fetus. The presence of autoimmune thyroid disorders, particularly Graves disease, is associated with other autoimmune conditions: Hashimoto thyroiditis, Addison disease, ovarian failure, rheumatoid arthritis, Sj¨ogren syndrome, diabetes mellitus (type 1), vitiligo, pernicious anemia, myasthenia gravis, and idiopathic thrombocytopenic purpura. Other factors that are associated with the development of autoimmune thyroid disorders include low birth weight, iodine excess and deficiency, selenium deficiency, parity, oral contraceptive pill use, reproductive age span, fetal microchimerism, stress, seasonal variation, allergy, smoking, radiation damage to the thyroid, and viral and bacterial infections (366).
Overt and subclinical hypothyroidism are defined as an elevated TSH with a low T4 and an elevated TSH and normal T4, respectively, using appropriate patient ranges (nonpregnant and pregnant). A number of professional organizations published various recommendations for thyroid function assessment via a TSH in women. Because of the long interval from development of disease to diagnosis, the nonspecific nature of symptoms, and the potential adverse neonatal and maternal outcomes associated with untreated hypothyroidism in pregnancy, the American Association of Clinical Endocrinologists (AACE) recommended screening women prior to conceiving or at the first prenatal appointment (367,368). The AACE also recommended screening for the presence of hypothyroidism in patients with type 1 diabetes mellitus (threefold increased risk of postpartum thyroid dysfunction and 33% prevalence overall), patients taking lithium therapy (35% prevalence), and consideration of testing in patients presenting with infertility (>12% prevalence) or depression (10% to 12% prevalence), as these populations are at an increased risk of hypothyroidism (368). A screening TSH was recommended in women starting at the age of 50 because of the increased prevalence of hypothyroidism in this population (369). Thyroid function testing at 6-month intervals was recommended for patients taking amiodarone, as hyperthyroidism or hypothyroidism occurs in 14% to 18% of these patients (368). Any woman with a history of postpartum thyroiditis should be offered annual surveillance of thyroid function, as 50% of these patients will develop hypothyroidism within 7 years of diagnosis (370). Because there is a high prevalence of hypothyroidism in women with Turner and Down syndromes, an annual check of thyroid function is recommended for these patients (371,372).