Vesico-vaginal fistula (VVF) is a devastating condition that causes physical, psychological and social disability for affected women, particularly in low-income countries [15]. Surgical repair is the primary treatment for this condition. Success rates vary according to the skill and experience of the surgeon, as well as the complexity of the fistula. In the present study, the success rate of surgical repair of OVVF was 83.02%. This success rate is close to the 85% set by the WHO to determine the level of quality of services offered to participants in a fistula treatment center [16]. A study conducted in Nord-Ubangi Province (in the DRC) by Paluku et al. reported an overall success rate of 87.1% for 163 consecutive repairs of OVVF [7]. Similarly, a retrospective analysis of 384 Congolese women undergoing surgical repair of VVF in Haut-Katanga Province (in the DRC) by Nsambi et al. [4] revealed an overall success rate of 82.8%. Similar high success rates were reported in several studies ranging from 84.3% to 94% [9, 17,18,19,20,21].

These differences in success rates could be explained by the clinical difference of the fistulas treated, the surgeons’ experience in fistula repair, the technical platforms used, the selection of cases of fistulas to be repaired, the choice of approach for the different cases of fistula repaired, and even the definition of surgical success, which differ from study to study.

Risk factor analysis for FSROVVF was based on comparison of women with FSROVVF and women without FSROVVF. Our results provide stronger evidence of the negative impact of pre-operative clinical fistula characteristics on surgical repair outcomes, as opposed to participant characteristics. In the present study, FSROVVF was significantly associated with scar fibrosis, the presence of two or more fistulas, fistula size > 3 cm, the presence of peri-operative hemorrhage and that of post-operative infection.

Our study found that scar fibrosis is a potential risk factor for repair failure. Several studies have demonstrated that the presence of scar fibrosis can reduce the chances of successful surgical repair of VVF [4, 18, 22, 23]. In a study by Nardos et al. [22], involving 268 participants undergoing surgical repair for OVVF, the presence of moderate to severe scar fibrosis was associated with a repair failure rate of 17%, compared with only 3% in participants with no scar fibrosis or mild fibrosis (AOR = 2.67; 95% CI: 1.58–4.50), concluding that scar fibrosis is an independent risk factor for VVF repair failure. A case–control study of risk factors associated with OVVF carried out on 420 women by Barageine et al. [24] in Uganda revealed that participants with severe scar fibrosis were 3.5 times more likely to suffer repair failure than those without scar fibrosis (AOR = 3.5; 95% CI: 1.6–7.6). Similarly, a study by Nsambi et al. [4] in Haut-Katanga province (in the DRC) reported that participants with scarring fibrosis were 15 times more likely to undergo repair failure than those without scarring fibrosis (AOR = 15.22; 95% CI: 7.34–31.58).

Scar fibrosis is a pathological process characterized by excessive scar tissue formation during lesion healing. Fibrosis can compromise the success of surgical repair of VVF in several ways. First, the presence of scar tissue can make dissection and closure of the fistula more difficult, increasing the chances of intraoperative complications such as bleeding and damage to surrounding structures. Second, fibrosis can restrict the mobility of surrounding tissues, which can lead to excessive tension on the suture and subsequent dehiscence of the repair [5, 18]. In addition, fibrous scarring can impair local vascularization, compromising normal healing and suture consolidation. Fibrosis can complicate surgical repair by making tissues less supple and more difficult to suture. Moreover, the presence of fibrosis can also increase the risk of fistula recurrence after surgery. It is therefore crucial for surgeons to consider the presence of scarring fibrosis when planning and performing surgical repair of vesico-vaginal fistula [22].

The presence of multiple fistulas may represent an additional challenge for surgical repair. The present study showed that the presence of two or more OVVFs in the same participant (AOR = 9.04; 95% CI: 3.01–27.13) and the association of an OVVF with other anatomoclinical fistula entities (AOR = 3.16; 95% CI: 1.09–9.13) were reported as significant predictors of FSROVVF. The Congolese study by Nsambi et al. [4] revealed that participants with two or more fistulas had a repair failure rate of 58.33% versus 12.54% in those with a single fistula (AOR = 7.41; 95% CI: 3.05—17.97), suggesting that the presence of multiple fistulas was an independent risk factor for failure of surgical repair of VVF. These authors point out that the presence of several fistulas in the same participant makes local tissue mobilization difficult and does not allow repair under tension due to the scarcity of tissue in the bladder [4].

For this reason, several authors suggest suturing the bladder and vagina separately without tension after separation of the vaginal plane from the bladder plane around the fistula. Wide separation of the two planes allows sufficient mobilization of the bladder  and permits tension-free suturing [4, 25]. The presence of multiple fistulas can lead to increased complexity of the surgical procedure, with additional difficulties associated with dissection, fistula closure and reconstruction of surrounding tissue. Furthermore, the presence of multiple fistulas may compromise local vascularization and increase the risk of tissue adhesions, which may lead to failure of surgical repair [18].

Previous studies [4, 18, 25] support the idea that fistula size > 3 cm is an independent risk factor for failure of surgical repair of VVF. In our study, participants with VVFs > 3 cm in size were more than 3 times, more likely to have failed repair than those with fistulas ≤ 3 cm in size (AOR = 3.65; 95% CI: 1.36–9.76).

This finding is identical to that of a Ugandan study by Kayondo et al. (OR = 6; 95% CI: 1.46–24.63) [5]. An Ethiopian study by Meikena et al. [26], which included 328 VVF participants, revealed a surgical repair failure rate of 3.5% for participants with fistula size ≤ 3 cm, while it was high at 15.6% for participants with fistula size > 3 cm (AOR = 11.68; 95% CI: 1.41–96.42). A larger fistula size can make the surgical procedure more complex, with additional challenges such as tissue manipulation, fistula closure and reconstruction of surrounding structures. In addition, larger fistulas may be associated with more extensive tissue loss and impaired vascularization, compromising successful repair [5]. Larger fistulas often pose greater challenges during surgical repair.

Closure often requires more complex techniques, including mobilization of surrounding tissue, skin or mucosa grafts, or even combined approaches. Poor vascularization of surrounding tissue can make it difficult for tissue grafts to heal and survive. In addition, excessive tension on the fistula closure can lead to tissue necrosis and dehiscence.

The present study found that participants with post-operative infection were more than 179 times more likely to have a FSROVVF (AOR = 178.89; 95% CI: 26.09–1226.64). Post-operative infection is a factor that has a significant negative impact on the outcome of surgical fistula repair, as also reported by Aynie et al. [10]. According to the Ethiopian study by Meikena et al. [26], participants who received antibiotic prophylaxis for 7 days in the peri-operative period had a repair failure rate of 8.2%, compared with 19.4% in those who did not receive prophylactic antibiotics, indicating that prevention of post-operative infection by antibiotics was a protective factor against FSROVVF (AOR = 0.125; 95% CI: 0.028–0.555).

Post-operative infections can compromise tissue healing and increase the risk of fistula recurrence. Post-operative infections can lead to complications such as increased suture dehiscence, delayed healing, pus accumulation and tissue inflammation, compromising fistula healing. In addition, infections can lead to further complications, such as abscess formation or sepsis, which can be life-threatening and require further medical intervention. To minimize the risk of post-operative infection and improve the outcome of surgical repair, it is essential to follow strict infection prevention protocols, such as administering prophylactic antibiotics, maintaining a sterile environment and careful monitoring for signs of infection posoperatively. Furthermore, a randomized controlled trial conducted in Benin concluded that women in the antibiotic prophylaxis group received fewer post-operative antibiotics and had fewer urinary tract infections, but that antibiotic prophylaxis did not reduce the chances of failed repair (OR = 2.1; 95% CI: 0.75–6.1) [27].

This study found a significant association between FSROVVF and peri-operative hemorrhage. Our results provide further evidence to support the role of peri-operative hemorrhage in predicting FSROVVF. Women with peri-operative hemorrhage were 7 times more likely not to have fistula closure than those without peri-operative hemorrhage (AOR = 7.01; 95% CI: 2.33–21.03). A recent Ugandan study by Holt et al. [28] reported that the rate of repair failure was significantly higher when a participant received peri-operative transfusion (AOR = 3.10; 95% CI: 1.11–8.66). The results of these studies highlight the negative impact of peri-operative hemorrhage on the outcome of surgical repair of VVF.

Hemorrhage can lead to reduced surgical visibility, difficulty in achieving accurate dissection and impaired suture quality. In addition, hemorrhage can increase the risk of post-operative complications such as infection and hematoma formation, which can compromise fistula healing. To minimize the risk of peri-operative hemorrhage and improve the outcome of surgical repair, it is essential to follow appropriate surgical protocols, such as mastering dissection and suturing techniques, using suitable surgical instruments and carefully monitoring for signs of hemorrhage during and after surgery.

FSROVVF is a major risk factor for poor participant quality of life. The ability to predict FSROVVF has always been the main concern of urologists and gynecologists repairing VVF. Accurate prediction of cases at risk of FSROVVF would make it possible to select cases meriting a higher standard of care, or more often, in our environment, early transfer to hospitals specializing in the management of VVF.

Thus, prediction of FSROVVF in at-risk participants must be sufficiently specific to avoid unnecessary referral. Hence the need for a predictive score to guide screening and the eventual decision-making process on where participants should undergo surgery. This means that decisions based on the scoring of score parameters using easy-to-collect clinical variables, as proposed in this article, can help avoid FSROVVF and repeat surgery.

Our study shows that the clinical score obtained by consolidation and scoring these six parameters proved to be the best model for identifying participants at risk of FSROVVF. Although moderately sensitive (61.11%), this score has a very high specificity (96.59%) and will therefore enable better detection of participants at risk of FSROVVF and seek to optimize surgical outcome (by referral to specialized centers). The advantage of the proposed score is that the clinical variables used can easily be identified during a routine pre-operative visit.

This score, after being validated in other populations, could be very useful in peripheral hospitals where participants with OVVF are recruited, to identify fistula women at risk of surgical repair failure and refer them to specialized referral hospitals for surgical care. Preventing FSROVVF thus means avoiding repeated and traumatic surgical interventions for participants, since the best chance for success is the initial attempt at repair. Every effort should be made to attain a successful result the first time, because each subsequent operation would create further sclerosis, making future attempts more difficult.

The strength of the present study is that it included a large number of participants with similar pathology in several provinces of the DRC. All participants benefited from the services of the same surgical team, with same expertise and using identical equipment. The same variables were taken from each participant and recorded.

However, as a limitation of this study, it is important to note that participants who remained incontinent at hospital discharge despite complete closure of their fistulas were classified as failures. It cannot be excluded that some of them became continent within weeks or months following surgery. The use of urodynamics during the discharge assessment and the review of these participants a few months after surgery would have made it possible to identify them and classify them as cured, thus increasing the success rate.