Genitourinary fistula is predominantly a childbirth-associated morbidity, whereby prolonged pressure of the fetus’s head during obstructed labour results in an abnormal passage between the vagina and bladder or between the vagina and rectum, resulting in urinary or faecal incontinence, or both. Fistulas resulting in urinary incontinence are most common, and are often referred to as genitourinary fistulas. Although the majority (80–95%) of genitourinary fistulas can be closed surgically,1
the likelihood of successful closure depends on the characteristics and severity of the fistula, skill of the surgeon and, probably, the surgical methods used. Many fistula surgeons have developed their own methods through experience2
; thus, perioperative procedures vary widely across surgeons and facilities. Few studies have examined the comparative effectiveness of different perioperative interventions related to the surgical management of genitourinary fistulas.3–13
One aspect of surgical repair in particular, the route of repair undertaken, is of critical research interest, as the abdominal (versus vaginal) approach may be associated with longer term hospitalisation,14
urinary tract infection (UTI)15
and increased blood loss.14,15
Recommendations vary with regard to whether a vaginal or abdominal surgical approach should be used for fistula repair. Vaginal approaches are generally thought to be appropriate for any fistula located between the bladder and the vagina,16,17
with some fistula surgeons claiming to be able to repair all fistulas by the vaginal route.18
However, abdominal approaches are also often considered to be most appropriate for ‘complex’ fistulas,14,19,20
with published indications for an abdominal route of repair including: a small-capacity or poorly compliant bladder which requires bladder augmentation14,17,19
; fistulas involving or close to the ureteric orifice (particularly if ureteric reimplantation is required)14,17,19
; vaginal stenosis or other factors inhibiting adequate vaginal exposure of the fistula14,17,19
; trigonal or supratrigonal location14
; intracervical location18
; and concomitant abdominal pathology.19
However, the choice of surgical approach remains, to some extent, a matter of surgeon preference or training19,21
and experience of the surgical team.14
Three retrospective studies have examined unadjusted associations between the route of surgery and repair outcomes. Kriplani et al.9
found a significantly higher proportion of continence (closed fistula with no residual incontinence) at discharge among fistulas repaired vaginally in their sample of 34 women. In contrast, Chigbu et al.,5
in their sample of 78 women with juxtacervical fistulas (which can be approached either vaginally or abdominally5
), found a higher proportion of fistula closure at discharge among women repaired abdominally (84.3%) than vaginally (77.8%); however, this difference was not statistically significant. Finally, Morhason-Bello et al.15
found no statistically significant differences in continence across 71 women with mid-vaginal fistula (with no fibrosis or evidence of infection, urethral or bladder neck involvement and without more than one previous repair) repaired either abdominally or vaginally; continence rates 3 months following surgery were 78.3% versus 80.0%, respectively. All three studies were probably underpowered to detect small differences, and examined only unadjusted associations (although the last two studies restricted the sample by type of fistula). Only Morhason-Bello et al. examined indications for vaginal versus abdominal or mixed vaginal and abdominal route of repair; the number of indications examined was limited because of the strict inclusion criteria employed.
A shared limitation of all three studies was the lack of adjustment for the potential imbalance of a range of prognostic features across comparison groups, also termed ‘confounding by indication’. In an observational study, the indication for a treatment may act as a confounder.22
For instance, a patient’s urinary fistula may have certain characteristics which indicate the need for an abdominal route of repair and, at the same time, these characteristics may also be associated with a poor repair prognosis. Consequently, treatments reserved for those with a poor prognosis will be statistically associated with worse outcomes, even when the treatment itself is beneficial.23
Although observational studies typically rely on methods such as statistical adjustment to minimise differences between comparison groups, confounding by indication may be less amenable to standard ways of accounting for confounding.23
For example, methods of controlling for noncomparability of comparison groups, such as disease severity scores, may not encompass the totality of factors that may influence both a provider’s decision with regard to the route of repair and eventual repair outcomes. This would result in incomplete adjustment and residual confounding.
Propensity score matching has been proposed as a method particularly suited for the control of confounding by indication. These methods are used to approximate the context of a randomised trial, insofar as treatment groups are comparable on measured confounding factors. Propensity score matching may thus minimise selection bias, as it maximises the comparability of individuals on a set of observed variables that may influence the provider’s decision to administer the treatment: in this case, route of repair.24
Importantly, however, propensity score matching cannot ensure comparability on unmeasured confounding factors.
Against this background, we conducted a secondary analysis on data from a multi-country prospective cohort study to elucidate the relationship between the route of repair and fistula closure. Our first aim was to evaluate which factors independently predicted the route of repair used, including the extent to which the choice of abdominal route was influenced by published indications for an abdominal route of repair. Second, we aimed to examine the influence of the route of repair on fistula closure, using both standard multivariable regression analysis and propensity score matching to account for potential confounding. Our third aim was to evaluate whether the effect of the route of repair on fistula closure varied by indication for repair.