Validation of a Model Predicting De Novo Stress Urinary Incontinence in Women Undergoing Pelvic Organ Prolapse Surgery

OBJECTIVE: To validate a previously developed prediction model for de novo stress urinary incontinence (SUI) after undergoing vaginal surgery for pelvic organ prolapse (POP). METHODS: Model performance was determined using a cohort of women who participated in two, 14-center randomized trials in the Netherlands that evaluated whether postoperative SUI 1 year after surgery was reduced with or without concomitant midurethral sling at the time of surgery for symptomatic women who had at least stage 2 POP. Age, number of previous vaginal births, urine leakage associated with urgency, history of diabetes, body mass index, preoperative stress test result, and placement of a midurethral sling were used to calculate the predicted probability of an individual developing de novo SUI. Predicted probabilities were compared with outcomes and quantitated using the concordance index and calibration curves. Model accuracy was compared with and without the preoperative stress test, and net reclassification improvement was measured using probability cutoffs of 0.2, 0.3, and 0.4. RESULTS: Of 239 participants who did not report preoperative SUI and underwent surgery, 152 were eligible for analysis with complete baseline and outcome data. Model discrimination was acceptable and consistent with performance in the original development cohort when the preoperative stress test result was included (concordance index 0.63; 95% CI 0.52-0.74) and had lower discrimination than when the stress test variable was not included (concordance index 0.57; 95% CI 0.46-0.67, P=.048). The model that included the stress test variable was most accurate when predicted probabilities of de novo SUI were between 0 and 50%, and it correctly reclassified upward 5.9% (95% CI -14.8 to 26.8) of participants with de novo SUI and correctly reclassified downward 16.9% (95% CI 6.6-27.7) of participants without de novo SUI. CONCLUSION: On external validation, the model was predictive of de novo SUI after vaginal prolapse surgery and may facilitate decision making regarding concomitant sling placement. CLINICAL TRIAL REGISTRATION: Nederlands Trial Register, NTRR 1197 en 1070.