The propensity for thyroiditis likely antedates pregnancy and, similar to other autoimmune endocrinopathies, a precipitating event such as a viral illness interplays with genetic and other factors. Careful scrutiny yields clinical and biochemical evidence of thyroid dysfunction in 5 to 10 percent of postpartum women. When postpartum thyroiditis develops, the majority of women are found to have thyroid peroxidase autoantibodies. Nevertheless, postpartum thyroiditis is diagnosed infrequently, largely because it typically develops after the traditional postpartum examination and because it results in vague and nonspecific symptoms. Such women are significantly more likely than euthyroid women to manifest depression and memory impairment.
There are two recognized clinical phases of postpartum thyroiditis (Table 75-1). Between 1 and 4 months after delivery, approximately 4 percent of all women develop transient destruction-induced thyrotoxicosis from excessive release of hormone from glandular disruption. The onset is abrupt, and a small, painless goiter is commonly found. Symptoms include fatigue and palpitations. Antithyroid medications such as propylthiouracil and methimazole are ineffective, and they may even hasten the development of a subsequent hypothyroid phase. Treatment usually is not necessary, but if symptoms are severe, a β-blocker may be administered. Approximately two-thirds of these women return directly to a euthyroid state, and the other third subsequently develop hypothyroidism.
TABLE 75-1. Clinical Phases of Postpartum Thyroid
Between 4 and 8 months postpartum, 2 to 5 percent of all women develop hypothyroidism. At least a third of such women will previously have experienced the thyrotoxic phase of postpartum thyroid dysfunction. Hypothyroidism can develop rapidly, sometimes within a month. Thus, women at risk for postpartum hypothyroidism should be evaluated regularly. If hypothyroidism develops, thyroxine replacement is initiated. It has been suggested that thyroxine be continued for 6 to 12 months and then gradually withdrawn.
About 33 percent of women who experience postpartum thyroiditis develop permanent hypothyroidism, which is much more common in women with thyroid peroxidase antibodies. The importance of long-term follow-up in these women is apparent.
For further reading in Williams Obstetrics, 23rd ed.,
see Chapter 53, “Thyroid and Other Endocrine Disorders.”