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.