Statistical analysis
The variables were presented as percentages for categorical variables, and as mean for continuous variables. We examined the baseline variables of the PCOS cohort and non-PCOS cohort by chi-square tests and student’s t-tests. The Kaplan-Meier method was used to acquire the cumulative incidence curve for the two cohorts. Log-rank test was also performed. The univariate Cox proportional hazard (PH) model was applied to estimate the hazard ratio and then adjusted the hazard ratio by multivariate Cox PH model. All statistical analyses were conducted with SAS 9.4 software (SAS Institute, Cary, NC, USA). P-value of less than 0.05 was regarded as significant.