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.