ORIGINAL ARTICLE: Postpartum thyroid dysfunction and the long‐term risk of hypothyroidism: results from a 12‐year follow‐up study of women with and without postpartum thyroid dysfunction

Background The long‐term risk of hypothyroidism following postpartum thyroid dysfunction (PPTD) is uncertain. Most previous studies have been small, short‐term or have lacked a control group. Objective To ascertain the long‐term risk of hypothyroidism in women following PPTD. Design and participants A 12‐year longitudinal study of 409 women (including 71 with PPTD) who previously participated in a PPTD prevalence study. Measurements The primary outcome measure was hypothyroidism (defined as TSH greater than 4 mU/l or on thyroxine replacement) at follow‐up. Outcomes in women with and without PPTD were compared by logistic regression. Receiver operating characteristic analysis was used to determine the optimal cut‐off for baseline TSH as a predictor of hypothyroidism in the cohort. Results At follow‐up, hypothyroidism was present in 27 of 71 women who had PPTD at baseline (38%) and 14 of 338 women without PPTD (4%). From multivariate analysis, odds ratios (with 95% confidence intervals) for hypothyroidism were – 4·8 (1·6, 14·1) for PPTD; 8·2 (2·8, 24·6) for positive thyroid peroxidase antibodies (TPOAb); 9·7 (2·6, 37·0) for the hypothyroid phase of PPTD and 51·4 (19·2, 137·5) for hypothyroid PPTD with positive TPOAb. A baseline TSH above 2·6 mU/l was the optimal cut‐off for predicting hypothyroidism (sensitivity 76%, specificity 86%). Conclusions PPTD is a strong predictor of hypothyroidism in the long‐term. Women who present with postpartum hypothyroidism or have positive TPOAb are at particularly high risk, suggesting that close long‐term follow‐up is advisable if thyroxine replacement is not instituted at an early stage.