Detection of obstetric anal sphincter injuries using machine learning-assisted impedance spectroscopy: a prospective, comparative, multicentre clinical study

Objective To evaluate the clinical performance and safety of the ONIRY system for obstetric anal sphincter injuries (OASI) detection versus three-dimensional endoanal ultrasound (EAUS). Design A prospective, comparative, multicentre, international study. Setting: Poland, Czechia, Slovakia, and Spain. Population 152 women between the first moments up to 8 weeks after vaginal delivery. Methods Participants underwent EAUS and were allocated to groups based on OASIS classification: A (no perineal tear), B (1st or 2nd degree tear), or C (3rd or 4th degree, anal sphincters affected). Electric impedance was measured in the anal canal using the ONIRY system. The primary endpoint was the diagnostic outcome of impedance spectroscopy versus EAUS. Adverse events were collected. Part II involved in silico modelling and 10-time 10-fold cross-validation for automated analysis. Main Outcome Measures Accuracy, sensitivity, and specificity. Results 30 women were allocated to group A, 61 to group B, and 61 to group C. The diagnostic outcome was determined for 147 participants. The accuracy, sensitivity, and specificity of the ML-assisted impedance spectroscopy were 87.0 ± 0.5%, 90.6 ± 2.0%, and 84.6 ± 1.9%, respectively, compared with EAUS. After data cleaning, the performance metrics of the proposed final ML model for ONIRY were: 90.0 ± 0.4%, 90.0 ± 1.2%, and 90.0 ± 0.7%, respectively. No adverse device effects or deficiencies were observed. Conclusion ML-assisted impedance spectroscopy offers a safe and accurate method for rapid OASI detection. This approach could effectively complement digital rectal examination in obstetric settings, supporting timely postpartum care. Funding information The study was financed by the Polish National Centre for Research and Development (POIR.01.01.01-00-0726/18). Key Message With 90% accuracy, the ONIRY system’s ML-assisted impedance spectroscopy offers a reliable, non-invasive method for detecting obstetric anal sphincter injuries, supporting timely postpartum diagnosis.