Study Strengths and Limitations
The strengths of this study include the careful efforts made to verify the study population to avoid selection bias. Because the sling type data were recorded only in unstructured text and could not be easily identified, an Obstetrics and Gynecology (OBGYN) physician (TFC) reviewed the operation records of all eligible patients to verify that these patients indeed received midurethral sling surgery. Another strength is that this study was able to examine the association between urodynamic parameters and surgical outcomes, as OBGYN physicians in CMUH regularly perform detailed urodynamic evaluations prior to surgery. Interestingly, a Cochrane review has concluded that urodynamic studies may change clinical decision making, but scant evidence shows that these evaluations improve clinical outcomes.45-47 In our unadjusted analysis, we identified that lower average flow rate and longer voiding time were associated with surgical complications, which, if validated in another study, may serve as quantitative indicators for a high risk of surgical complications.
This study has several limitations. First, residual and unmeasured confounders could not be entirely excluded. For example, we may have misclassified patients with menopausal syndrome as being without menopausal syndrome, because we were reliant on ICD records from different doctors and from a retrospective single center database. Therefore, the effects of potential risk factors (such as patient lifestyle factors, physician bias and experience with recording menopausal symptoms) may have been slightly overestimated due to the underestimation of these positive confounders. Second, the standard protocol for follow-up is usually 6 months following surgery; we may have misclassified patients with surgical complications as instead belonging to the group without complications, because these patients may not come back to our hospital for care so were lost to follow-up. Third, the associations found in our study do not guarantee causality. Our findings were not verified in other populations under different healthcare systems and the results should be externally validated to prove generalizability.