Progesterone use may increase risk for thyroid cancer in wom
Researchers conducted a retrospective population-based study of 146,024 women with infertility aged 20 to 45 years living in Denmark from 1995 to 2017. Information on infertility status and fertility drug use was collected from the Danish Infertility Cohort. Participants were followed until the occurrence of thyroid cancer, any other cancer, death, emigration, total thyroidectomy or the end of the follow-up period on Dec. 31, 2018.

Of the cohort, 88.6% used fertility drugs during the study period, and 167 were diagnosed with thyroid cancer. The median time from infertility diagnosis to thyroid cancer diagnosis was 9.1 years. Of those diagnosed with thyroid cancer, 84% had papillary thyroid cancer and 13% had follicular thyroid cancer. Progesterone users had an increased risk for thyroid cancer within the first 5 years of fertility drug use compared with nonusers (aHR = 1.61; 95% CI, 1.01-2.56).