How common is postpartum thyroiditis? A methodologic overview of the literature

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Abstract
• The incidence of postpartum thyroiditis (PPT) in the general population has been reported to range from 1.9% to 16.7%, depending on the study. To determine whether bias may have played a role in the generation of these widely varying estimates, a set of methodologic criteria were applied to the published original research dealing with the epidemiology of PPT. The articles that passed these methodologic filters reported a narrow range of incidences of PPT, varying between 3.7% and 5.9%. Reanalysis of these articles confirmed that thyrotoxicosis occurred more frequently in the first 3 months post partum than did hypothyroidism, and that a positive antimicrosomal antibody titer was strongly associated with postpartum thyroid dysfunction (odds ratio, 86.6; 95% confidence interval, 45.9 to 163.2). This article suggests that PPT is a common condition that occurs in the postpartum period. The best estimate of the incidence of PPT in an unselected cohort of postpartum women is 4.9%. (Arch Intern Med. 1990;150:1397-1400)