Context: The incidence of postpartum thyroiditis (PPT) varies widely in the literature. Limited data exist concerning the hormonal status of women with PPT at the end of the first postpartum year.
Objective: Our aim was to conduct a large prospective study of the incidence and clinical course of PPT.
Design: A total of 4394 women were screened for thyroid function and thyroid autoantibodies at 6 and 12 months postpartum. Women were classified as being at high or low risk of having thyroid disease before any thyroid testing.
Setting: The study was conducted at two ambulatory clinics in southern Italy, an area of mild iodine deficiency.
Patients: A total of 4394 pregnant women were studied.
Intervention: There was no intervention.
Main outcome measures: We measured incidence, clinical presentation, and course of postpartum thyroiditis.
Results: The incidence of postpartum thyroiditis was 3.9% (169 of 4384). Women classified as being at high risk for thyroid disease had a higher incidence of PPT than women classified as low risk (11.1 vs. 1.9%; odds ratio, 6.69; 95% confidence interval, 4.63, 9.68). Eighty-two percent of the 169 women with PPT had a hypothyroid phase during the first postpartum year. At the end of the first postpartum year, 54% of the 169 women had persistent hypothyroidism.
Conclusions: One of every 25 women in southern Italy developed PPT. Women at high risk for thyroid disease have an increased rate of PPT. The high rate of permanent hypothyroidism at 1 yr should result in a reevaluation of the widely held belief that most women with PPT are euthyroid at the end of the first postpartum year.
Trial registration: ClinicalTrials.gov NCT00846755.