Geographic Access Barrier as a Critical Mediator in Obstetric Fistula Treatment Cascade in Nigeria: Evidence from a Causal Mediation Analysis of 5,496 Cases

Background: Approximately two million women globally currently live with untreated obstetric fistula, predominantly in sub-Saharan Africa and South Asia, with Nigeria accounting for 40% of cases. Despite the recognition of multiple healthcare barriers, the causal mechanisms through which these barriers affect treatment-seeking behavior remain poorly understood. We conducted a causal mediation analysis to examine potential pathways in the fistula treatment cascade. Methods: We analyzed data from 5,496 women who reported fistula symptoms in the 2024 Nigeria Demographic and Health Survey. Using the counterfactual framework for causal mediation, we decomposed the relationship between fistula knowledge (exposure) and treatment-seeking (outcome) into direct and indirect effects operating through three mediator domains: financial, geographic access, and autonomy barriers. We estimated natural direct and indirect effects using Baron and Kenny regression with product-of-coefficients method, inverse probability weighting, and doubly robust estimation. Bootstrap confidence intervals (1,000 replications) and E-value sensitivity analyses were used to assess the robustness of sampling variability and unmeasured confounding. Results: Among women with fistula, 65.0% sought treatment, 3.3% received surgical repair, and 6.9% achieved resolution leaving 93.1% with unresolved fistula. The largest cascade gap (61.7%) occurred between treatment-seeking and surgery receipt. Geographic access barriers significantly reduced treatment-seeking (OR=0.73; 95% CI: 0.59-0.88; p=0.002), emerged as the only significant mediating pathway (indirect effect β=-0.19; 95% CI: -0.33 to -0.07). Financial barriers (OR=1.11; 95% CI: 0.95-1.31) and autonomy barriers (OR=0.99; 95% CI: 0.84-1.18) were not independently associated with treatment-seeking in adjusted models. The E-value for geographic access barriers was 2.08, indicating moderate robustness to unmeasured confounding. Conclusion: Geographic access barriers emerged as the dominant pathway associated with reduced treatment engagement, findings consistent with these barriers suggesting a critical pathway under stated causal assumptions. Although knowledge was not directly associated with treatment-seeking, mediation models suggested that geographic access barriers were the only pathway consistently linked to care engagement. Financial and autonomy-related barriers were not statistically significant mediators in this analysis, though this may reflect measurement limitations or operation at different cascade stages rather than true irrelevance. The primary cascade bottleneck is surgical access rather than treatment-seeking, suggesting health system capacity constraints. These findings align with a causal interpretation under the stated identification assumptions of the counterfactual framework, though temporal ordering cannot be definitively established from cross-sectional data. Interventions should prioritize mobile surgical outreach, transportation vouchers, and decentralizing fistula repair services.