A model for predicting the risk of de novo stress urinary incontinence in women undergoing pelvic organ prolapse surgery

Abstract

Objective: To construct and validate a prediction model for estimating the risk of de novo stress urinary incontinence (SUI) after vaginal pelvic organ prolapse (POP) surgery and compare it with predictions using preoperative urinary stress testing and expert surgeons' predictions.

Materials and methods: Using the data set (n=457) from the Outcomes Following Vaginal Prolapse Repair and Midurethral Sling trial, a model using 12 clinical preoperative predictors of de novo SUI was constructed. De novo SUI was determined by Pelvic Floor Distress Inventory responses through 12 months postoperatively. After fitting the multivariable logistic regression model using the best predictors, the model was internally validated with 1,000 bootstrap samples to obtain bias-corrected accuracy using a concordance index. The model's predictions were also externally validated by comparing findings against actual outcomes using Colpopexy and Urinary Reduction Efforts trial patients (n=316). The final model's performance was compared with experts using a test data set of 32 randomly chosen Outcomes Following Vaginal Prolapse Repair and Midurethral Sling trial patients through comparison of the model's area under the curve against: 1) 22 experts' predictions; and 2) preoperative prolapse reduction stress testing.

Results: A model containing seven predictors discriminated between de novo SUI status (concordance index 0.73, 95% confidence interval [CI] 0.65-0.80) in Outcomes Following Vaginal Prolapse Repair and Midurethral Sling participants and outperformed expert clinicians (area under the curve 0.72 compared with 0.62, P<.001) and preoperative urinary stress testing (area under the curve 0.72 compared with 0.54, P<.001). The concordance index for Colpopexy and Urinary Reduction Efforts trial participants was 0.62 (95% CI 0.56-0.69).

Conclusion: This individualized prediction model for de novo SUI after vaginal POP surgery is valid and outperforms preoperative stress testing, prediction by experts, and preoperative reduction cough stress testing. An online calculator is provided for clinical use.

Level of evidence: III.

Figure 1

Nomogram for predicting the probability of de novo stress urinary incontinence (SUI) for women who undergo surgery for pelvic organ prolapse. The first row (Points) is the point that is assigned to each variable's measurement from rows 2–8, which are the variables that are included in the predictive model. The assigned points for all 7 variables are then summed up and the total can be located on line 9 (Total Points). Once the Total Points are located draw a vertical line down to the bottom line to obtain the predicted probability of de novo stress urinary incontinence (SUI).

Figure 2

Calibration curve for a model predicting risk of developing De novo stress urinary incontinence (SUI) after surgery for pelvic organ prolapse.

Figure 3

Receiver Operating Characteristic (ROC) curves generated when measuring the accuracy of the logistic models’ predictions using actual outcomes from patients from the Outcomes Following Vaginal Prolapse Repair and Midurethral Sling (2) study (internal validation = green) and the Colpopexy and Urinary Reduction Efforts (7) study (external validation = red).

Figure 4

Comparing accuracy of the models’ predictions, experts’ predictions and the preoperative stress test results using Receiver Operating Characteristic (ROC) curves in predicting De novo stress urinary incontinence (SUI)for 32 random patients selected from the Outcomes Following Vaginal Prolapse Repair and Midurethral Sling dataset. The model was significantly more accurate than experts who had knowledge of the same patient characteristics and preoperative prolapse reduction stress test results. The model was also significantly more accurate than the preoperative prolapse reduction stress test alone.

Figure 5

Scatter plot of the models’ predicted probabilities against the experts’ predicted probabilities. The solid diagonal line indicates perfect agreement between predictions. Experts’ predictions demonstrate increased variability as the model's predicted probabilities increase. For example, at predicted probabilities of De novo stress urinary incontinence (SUI)between 30%–50% the range of the experts’ predicted probabilities was highly variable and ranged from 0% to 100%.