Diagnostic accuracy of Impedance Spectroscopy versus Digital Rectal Examination for Obstetric Anal Sphincter Injuries: a postpartum post-hoc analysis

Accurate diagnosis of obstetric anal sphincter injuries (OASIs) is critical for timely repair and prevention of long-term morbidity, yet digital rectal examination (DRE) remains insufficiently sensitive. In this post-hoc analysis of a prospective multicentre diagnostic study (NCT04903977), we compared the diagnostic performance of DRE and machine learning-assisted impedance spectroscopy with three-dimensional endoanal ultrasound (EAUS) as the reference. A total of 152 women who delivered vaginally were assessed up to 8 weeks postpartum. DRE demonstrated a sensitivity of 44.3%, specificity of 83.5%, and overall accuracy of 67.8%. Impedance spectroscopy achieved 90.6% sensitivity, 84.6% specificity, and 87.0% accuracy against EAUS. DRE frequently fails to detect OASIs postpartum. A minimally invasive, operator-independent impedance-based method significantly improves diagnostic sensitivity and warrants further evaluation for use immediately after delivery to enable timely primary repair.