Postpartum thyroid dysfunction in women with normal thyroid function during pregnancy

The aim of this study was to establish the risk of postpartum thyroid dysfunction (PPTD) in women who had normal thyroid function during pregnancy and no history of thyroid disease.

Four thousand and twenty-two consecutive pregnant women were screened for thyroid function and antithyroid antibody. Among women with normal thyroid function during pregnancy and no history of thyroid disease, thyroid function were assessed in 131 of 388 antithyroid antibody positive (Group I) and 1030 of 3503 antibody negative (Group II) women at 1 and 3 months postpartum. In Group I women who experienced PPTD, the frequency of later manifestation of Hashimoto's disease was compared according to titres of antithyroid antibodies.

Blood samples in early pregnancy, and at 1 month and 3 months postpartum were obtained using the dried blood spot method. Levels of fT4 were measured by RIA, TSH by fluoroimmunoassay or ELISA, antimicrosome antibody (AMC) and antithyroglobulin antibody (ATG) by indirect agglutination reactions.

The prevalence of PPTD at 1 month and 3 months postpartum were found to be 6.9% and 21.3% in Group I, and 5.3% and 4.7% in Group II, respectively. The prevalence of PPTD was significantly higher at 3 months postpartum in Group I (P<0.05). 27.3% of women with PPTD in Group I were later found to have Hashimoto's disease and 9.1% manifested hypothyroidism without goitre. A high AMC titre (> or = 25600) at 3 months postpartum in women with PPTD was related to the manifestation of Hashimoto's disease. AMC titres of PPTD women and women who developed Hashimoto's disease were significantly higher than those of control women who did not experience PPTD.

A high prevalence of PPTD was found in women with antithyroid antibodies who were euthyroid during pregnancy. Prolonged follow-up of the subsequent thyroid function may be needed in women who experience PPTD and/or show a high titre of antithyroid antibody.