External validation of the endometriosis fertility index (EFI) for predicting spontaneous pregnancy after surgery: Further considerations on its validity

Background/Aims: The revised American Society for Reproductive Medicine classification of endometriosis has a limited predictive value for pregnancy after surgery. A tool for predicting spontaneous pregnancy or pregnancy following assisted reproduction technology (ART) represents a clinical need. This study aimed to (i) provide an external validation of the EFI score in predicting pregnancy in infertile Italian endometriosis women; (ii) evaluate the predictive value of EFI score on ART outcome for patients who previously attempted to spontaneously conceive after surgery. Methods: In 104 women with endometriosis, EFI score was calculated based on a prospective database data. Cumulative pregnancy rates curves were calculated using Kaplan-Meier (K-M) product limit estimate and log-rank test was used to evaluate differences between EFI groups. A receiver operating characteristic (ROC) curve was plotted for EFI as a predictor of ART outcome. Results: Differences in time to non-ART pregnancy for the six EFI groups were statistically significant (log-rank, p = 1.4 × 10^-4). The area under the curve (AUC) for EFI as ART outcome predictor was 0.75 (95% CI 0.61-0.89, p = 6.2 × 10^-3), while the best cut-point for pregnancy was 5.5. Conclusion: The EFI score is a reliable scoring system to predict non-ART and ART pregnancy outcome after surgery for endometriosis.