Hypothesis / aims of study
The prevalence of stress urinary incontinence (SUI) in women is high and several risk factors account for its frequency. Overweight and obesity are independent risk factors frequently found in this population. Also, obesity increases the non-successful treatment in patients with SUI that undergo tension free mid-urethral sling surgery. Several retrospective and prospective studies have evaluated the objective and subjective cure rates in obese women, however those have been inconclusive and there are not meta-analysis available. The goal of this study was to perform a systematic review and meta-analysis of the literature, to evaluate the subjective and objective cure rates in obese women with SUI after tension free mid-urethral sling surgery.
Study design, materials and methods
A literature search with the terms ("urinary incontinence") OR ("urinary" AND "incontinence") OR ("urinary incontinence" AND "obesity") OR ("obesity" AND "sling") OR ("urinary incontinence" AND "obese" AND "clinical trial") in OVID, MEDNAR, Embase, Scopus, Web of Science and PubMed databases was conducted. A total of 219 articles were found and evaluated. The non-randomized control trials and the gray literature were excluded. Finally, 5 randomized controlled trials that compared subjective and objective cure rates in normal and obese patients who underwent tension free mid-urethral sling surgery, were identified and evaluated for risk of bias under the Cochrane Handbook for Systematic Reviews of Interventions (The Cochrane Collaboration, 2018). Two studies were excluded; one due to the high risk of bias and the other one due to lack of information. The literature search was organized according to the PRISMA flow diagram (The PRISMA Statement, 2009) (figure 1). Patients were stratified according to their body mass index (BMI) as obese (>30 kg/m2) and non-obese (<30 kg/m2). The subjective cure rate was evaluated with questionnaires and the patients perception of leakage during the day, while the objective cure rate was evaluated with pad test, cough test and urodynamic study. Meta-analysis of dichotomous data (cure vs. failure) under random effects model was performed using Review Manager 5.3 (The Cochrane Collaboration, 2014) for subjective and objective evaluation groups. Heterogeneity test (I2) and risk ratio (RR) were evaluated. A p-value < 0.05 was considered statistically significant.
The three randomized control trials included in the meta-analysis involved 865 patients, 566 obese and 299 non-obese for the subjective evaluation and 873 patients, 558 obese and 315 non-obese for the objective evaluation, all women older than 50 years-old with diagnosis of SUI treated with tension free mid-urethral sling. Events were considered as failure of treatment. The meta-analysis of subjective cure rate disfavours obese women [RR 0.49 (0.31 - 0.77), p = 0.002], however, the test of heterogeneity shows a significant p-value (p = 0.04) (figure 2.A). Also, objective cure rate disfavours obese women [RR 0.62 (0.48 - 0.79), p = 0.0001] with a non-significant heterogeneity (p = 0.46) (figure 2.B).
Interpretation of results
There is high heterogeneity among studies to show a statistical significant difference in subjective cure rates among obese and non-obese women who underwent sling surgery that cannot be explained by chance alone. On the other hand, the objective cure rate showed an heterogeneity non-statistically significant (p = 0.46), which means the heterogeneity that can be found is explained by chance, the data is relevant and all the studies were comparable. The results evidenced a Risk Ratio of 0.62 understood as a risk reduction of failure in non-obese patients of 38%.