Study population
This cohort study was conducted retrospectively from 2000 to 2013. Female with newly diagnosed with polycystic ovary syndrome (PCOS), with at least two outpatient visits or once admission record, were enrolled as PCOS cohort. The inclusion criteria were female aged from 20 to 50 years old, and have never been diagnosed with Graves’ disease before. We exclude patients with a history of thyroid diseases or comorbidities that might have caused Graves’ disease: congenital hypothyroidism (ICD-9-CM code 243), postsurgical hypothyroidism (ICD-9-CM code 244.0), other postablative hypothyroidism (ICD-9-CM code 244.1), iodine hypothyroidism (ICD-9-CM code 244.2), other iatrogenic hypothyroidism (ICD-9-CM code 244.3), iatrogenic thyroiditis (ICD-9-CM code 245.4), and thyroid dysfunction (ICD-9-CM code 648.1). The PCOS-free female was recruited as the PCOS-free cohort. We matched one PCOS patient to four PCOS-free patients according to age and index year. The index date was designed to be the first date of PCOS diagnosis for PCOS cohort, and a random date between 2000 and 2012 for the PCOS-free cohort. We observed the participant until they started a Graves’ disease event, loss of follow-up, or the end of the study, whichever came first.