The Use of Transperineal and Endoanal Ultrasound in Diagnosis and Management of Obstetric Anal Sphincter Injuries (OASIs): A Narrative Review from a Gynecologic Perspective

Obstetric anal sphincter injuries (OASIs) are serious complications of vaginal delivery and the most frequent cause of postpartum anal incontinence. Underdiagnosis during delivery persists due to limited availability of accurate imaging. Transperineal ultrasound (TPUS) and endoanal ultrasound (EAUS) enable structural assessment of the anal sphincter and have growing roles in triage, repair planning, and follow-up.The aim of the present review is to integrate current evidence on diagnostic value, clinical usefulness, and potential implementation of TPUS and EAUS in gynecologic practice.Ultrasound identifies a high burden of occult sphincter trauma in primiparas with normal clinical assessment with rates close to 25%. EAUS is currently the gold standard for accurate imaging of defects. TPUS has excellent diagnostic performance for external anal sphincter (EAS) defects and is practical for bedside use. Improving the diagnosis of OASIs requires structured post-delivery clinical examination combined with selective use of TPUS as a first-line imaging modality and EAUS in cases of diagnostic uncertainty or suspected complex injury.Immediate postpartum ultrasound may help reduce delayed diagnoses and support timely surgical repair. Key barriers include operator dependence, training, availability, and variable image quality, particularly for routine EAUS in the labor ward.Incorporating ultrasound into postpartum management improves detection and classification of OASIs and subsequently repair and prognosis. Currently, judicious application in high-risk deliveries seems to be an appropriate approach until more evidence from prospective and economic studies is available. New technologies (3D/4D imaging, standardized terminology, and decision-support/AI) hold promise to increase reproducibility and use in everyday clinical practice.