4.5 | Strength and limtations
Several limitations should be considered when interpreting the results of this study. First, the definition of UL was not based on imaging, but instead, on ICD-10 codes and outpatient clinic visits. Since UL is mostly asymptomatic in early stages, women who have asymptomatic UL may have been undiagnosed, which may cause the prevalence of UL to be underestimated. Second, information about the size and number of ULs was not available due to the database characteristics. Third, gynecologic information, including parity, presence of polycystic ovarian syndrome, or hormonal status, were also inaccessible; these factors can affect the development of type 2 diabetes mellitus, and their absence lowers the generalizability of our results. Finally, because this study was conducted using the Korean nationwide database, the results might not be generalizable to other ethnicities. However, this study is valuable because, to our knowledge, it is the first large-scale, longitudinal study to evaluate the association between presence of UL and development of type 2 diabetes mellitus in young women.