Use of endoanal ultrasound in detecting obstetric anal sphincter injury immediately after birth

INTRODUCTION: Obstetric anal sphincter injury (OASI) complicates around 5% of deliveries in primiparas. The study objective was to assess the utility of three‐dimensional endoanal ultrasonography (3D‐EAUS) in the diagnosis of OASI. MATERIAL AND METHODS: The present study was designed to mirror screening settings with an unselected cohort of nulliparous women. All enrolled patients underwent clinical examination of the perineum by the caregiver, and 3D‐EAUS was conducted. Post‐processing of ultrasonography volume data was performed by an experienced colorectal surgeon who was blinded to all other data. The sensitivity, specificity, negative predictive value, and positive predictive value of 3D‐EAUS in the diagnosis of OASI was evaluated. The trial is registered at ISCRTN: 18006769. RESULTS: A total of 680 scans were performed, of which 18.5% were judged as “non‐assessable”, resulting in 554 assessable recordings. Sphincter defects were observed in 12.8% of all assessable recordings on 3D‐EAUS (n = 71). With clinical examination set as the reference standard, ultrasound sensitivity in the diagnosis of OASI was 30.4%, whereas its specificity was 87.9%. The negative predictive value was 96.7% and the positive predictive value was only 9.9%. Comments were left on 175 examinations, of which 74% referred to the management of the examination. CONCLUSIONS: Using 3D‐EAUS in a maternity ward is demanding because staff generally have little experience in endoanal ultrasound, which contributes to difficulties in obtaining good image quality. When 3D‐EAUS is performed to mirror screening settings, it adds no convincing diagnostic power to clinical examination in the diagnosis of OASI.