Increased risk of thyroid disease in Danish women with polycystic ovary syndrome: a cohort study

Aim: To investigate risk of thyroid disease in Danish women with PCOS. Design: National register-based study on women with PCOS in Denmark. 18,476 women had a diagnosis of PCOS in the Danish National Patient Register. PCOS Odense University Hospital (PCOS OUH, n = 1146) was an embedded cohort of women with PCOS and clinical and biochemical examination. Three age-matched controls were included for each woman with PCOS (n = 54,757). The main outcome measures were thyroid disease (hypothyroidism, Graves' disease, goiter, thyroiditis) according to hospital diagnosis codes and/or inferred from filled medicine prescriptions. Associations between baseline TSH and development of cardio-metabolic disease was examined in PCOS OUH. Results: The median (quartiles) age at inclusion was 29 (23-35) years and follow-up duration was 11.1 (6.9-16.0) years. The hazard ratio (95% CI) for thyroid disease development was 2.5 (2.3-2.7) (P < 0.001). The event rate of thyroid disease was 6.0 per 1000 patient-years in PCOS Denmark versus 2.4 per 1000 patient-years in controls (P < 0.001). Women in PCOS OUH with TSH >= 2.5 mIU/L (n = 133) had higher BMI (median 29 vs 27 kg/m(2)), wider waist, higher triglycerides and free testosterone by the time of PCOS diagnosis compared to women in PCOS OUH with TSH <2.5 mIU/L (n = 588). Baseline TSH did not predict later development of cardio-metabolic diseases in PCOS OUH. Conclusions: The event rate of thyroid disease was significantly and substantially higher in women with PCOS compared to controls.