The link between obesity and female stress urinary incontinence (SUI) is well established. Obesity results in elevated intra-abdominal pressure, leading to pelvic floor denervation and weakened musculature. Mid-urethral sling (MUS) procedures are commonly performed surgeries for SUI. Studies have shown varying MUS success in population groups with high-risk factors, like obesity and intrinsic sphincter deficiency (ISD). Literature on surgical outcomes of all three generations of MUS on overweight and obese patients remains lacking, limiting clinicians’ ability to individualize pre-operative counseling and decision making. Our primary objective was to evaluate surgical outcomes in overweight and obese patients with USI (urodynamic stress incontinence) treated with various MUS compared to normal weight patients. Our secondary objective was to identify risk factors predicting MUS failure in this population.

Records of 688 women between January 2004 and July 2017 were retrospectively reviewed. Women who underwent MUS surgery for USI were included. Women were excluded if they had SUI symptoms without demonstrable USI on urodynamic studies (UDS), ≥ stage II genital prolapse in all compartments according to POP-Q, detrusor overactivity, mixed incontinence, neurogenic bladder dysfunction, post-void residual urine >100ml, or received concurrent prolapse surgery. All 3 generations of MUS (single incision slings, trans-obturator and retropubic tapes) were utilized. Paired-samples t-test and either ANOVA, chi-squared, McNemar’s, and Fisher exact tests were used to analyze continuous and categorical data, respectively. Patients received UDS, one-hour pad test, Urogenital Distress Inventory-6 (UDI-6) and Incontinence Impact Questionnaire-7 (IIQ-7), and were divided into normal weight, overweight, and obese. Objective cure at 1-year was defined as no involuntary urine leakage during filling cystometry and pad test <2grams. Subjective cure was established by negative response to question 3 on UDI-6.

729 women underwent MUS surgeries during the study period. 41 were excluded due to incomplete data. 688 patients were included in our final analysis. Slightly over half our cohort was overweight or obese (n= 264 and 75 respectively). 57% (199/349), 41% (109/264) and 45% (34/75) of normal weight, overweight and obese patients respectively received SIS surgery. TOT surgery was performed in 32% (113/349), 42% (112/264) and 43% (32/75) of normal weight, overweight and obese patients respectively. The remaining 11% (37/349), 16% (43/264) and 12% (9/75) of normal weight, overweight and obese patients respectively received MUS-r surgery. There were no significant differences in age, parity, menopausal status, previous history of prolapse or anti-incontinence surgery, pre-operative ISD, urethral function, operating time, blood loss, hemoglobin change, duration of hospitalization, and surgical complications between the 3 groups. Overweight and obese patients had a significantly higher prevalence of diabetes mellitus (DM) compared to normal weight patients (18.9% and 26.7% versus 8.9% respectively, p <0.001). UDI-6 and IIQ-7 scores reflected significant QOL improvement pre- and post-operatively in all patients (Table 2). The obese group had significantly worse UDI-6 and IIQ-7 scores pre- and post-operatively compared to normal weight and overweight groups, although score improvement was similar in magnitude across all 3 groups. There were no significant differences in pre- and post-operative DO, BOO and urodynamic parameters. At 1-year follow-up, the overall objective and subjective cure rates were 88.2% and 85.9% respectively. There was a significantly higher rate of persistent USI in the overweight and obese groups compared to the normal weight group (12.1% and 21.4% versus 7.7% respectively). 6 patients developed post-operative detrusor overactivity incontinence with pad test ≥ 2grams – 3 in the normal weight group, 1 in overweight group and 2 in obese group. Table 3 shows the significantly lower overall objective and subjective cure rates (76% and 70.1% respectively) in the obese group compared to normal weight (91.4% and 89.1% respectively) and overweight (87.5% and 86% respectively) groups. With regards to the sling used, obese patients had significantly lower objective cure rates with all slings except TOT, and significantly lower subjective cure rate with all slings except MUS-r. The clinical features of patients in the overweight and obese groups stratified into MUS success and failure groups. Factors that were more common in obese patients with failed MUS surgery were analyzed via univariate logistic regression and included age ≥ 66 years (OR 1.72), menopause (OR 4.77), previous prolapse surgery (OR 4.19), and presence of DM (OR 2.34). A common factor present in both overweight and obese patients was a pre-operative diagnosis of ISD (OR 4.67, p<0.001 and OR 4.86, p= 0.001 respectively).

Our results showed an adverse impact of obesity on the overall objective and subjective MUS success rates, with no effect on operative complications. It is worthwhile noting that majority of existing literature has focused on TVT and/or TOT. Our study has thus shed light on aspects lacking in previous publications. Interestingly, while we found consistently lower objective and subjective cure rates in obese patients across all SIS types, there was no difference in objective and subjective success rates for TOT and MUS-r respectively across all 3 BMI groups. Our study also showed that obese patients experienced greater severity of bother of USI with impact on their QOL at baseline and 1-year post-operatively compared to their normal weight and overweight counterparts, although the magnitude of UDI-6 and IIQ-7 score improvements were similar across all 3 groups. We found that MUS failures were more likely to occur in obese women who were elderly (age ≥ 66 years), diabetic, menopausal, with previous prolapse surgeries and pre-operative ISD, of which the latter 3 factors each accounted for a greater than 4-fold increased risk of failure at 1-year. Age and menopausal status are closely intertwined factors implicated in the pathophysiology of SUI. DM was identified in our cohort, it may have been a confounder given its higher baseline prevalence in the overweight and obese groups. We found previous prolapse surgery and ISD to be significant risk factors, with the latter found to have over 4-fold increased risk for MUS failure in both overweight and obese groups.

Obese women with MUS had lower objective and subjective cure rates at 1-year, and worse quality-of-life scores compared to normal weight and overweight women. Risk factors for failure include old age, diabetes, menopause, previous prolapse surgery and ISD. Surgeons should incorporate this information for individualized patient counseling as part of informed consent process.