Anal sphincter injuries occurring during natural deliveries are often a reason for severe complications, including fecal incontinence. Currently, approximately 80% of these injuries remain unrecognized. Therefore, it is crucial to focus on finding a way to diagnose such injuries as early as possible to apply the tailored treatment. This study aimed to assess the accuracy of impedance spectroscopy in the diagnostics of obstetric anal sphincter injuries (OASIs) using a specially designed rectal probe called the ONIRY Probe. The protocol of the clinical trials is described at NCT03769792. Twenty women after natural delivery were enrolled in the study and divided into two groups referring to the stage of a perineal tear (Group A: 1- or 2-degrees, and Group B: 3- or 4-degrees of a perineal tear; without or with sphincter injury, respectively). The study design included three visits during which a number of diagnostic tests were performed, including impedance spectroscopy, and 3-dimensional endoanal ultrasound, anorectal manometry, and physical examination as a reference. Statistical analysis comprised raw data analysis, as well as post-processing with the Synthetic Minority Oversampling Technique (SMOTE) method, as the output reference grade was highly imbalanced. A variety of machine learning techniques were applied for the OASI classification (≤2 vs. >2), and Wexner scale (=0 vs. >0). The best efficacies were obtained using Random Forest and k-Nearest Neighbors methods. Best accuracies were 93.3% and 99.6%, for raw and re-analyzed data, respectively, for ultrasound assessed by the OASI classification; and 79.8% and 97.0%, respectively, for clinical evaluation using the Wexner scale. Impedance spectroscopy performed using the ONIRY Probe appears to be a promising diagnostic technique for anal sphincter injury detection but requires further investigation (the next phase of the pilot clinical trial is described at NCT04181840).
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