2.2 | Study design and participants
We selected 2,755,790 women aged between 20 and 40 years at baseline who underwent at least one health checkup between 2009 and 2012. The time point at the first health checkup for each patient between 2009 and 2012 was considered the index date. We excluded those who were previously diagnosed with type 2 diabetes mellitus (n = 28,136), those diagnosed with type 2 diabetes mellitus within the first year of entry (n = 1,607), those who had uterine myomectomy during the study period (n = 18,485), and those with missing data for least 1 variable (n = 166,012). Finally, a total of 2,541,550 patients were eligible for inclusion and were followed until December 31, 2018.