Detecting postpartum anal sphincter injuries with three-dimensional endoanal ultrasound: a prospective diagnostic study

Abstract

Occult obstetric anal sphincter injury (OASIS) is the subject of much debate. Three-dimensional endoanal ultrasound (3D-EAUS), regarded gold standard for anal sphincter evaluation in non-obstetric settings, is suggested to be a better tool for evaluation of OASIS than routine clinical examination. The aim of this study was to compare routine postpartum clinical examination with 3D-EAUS for detecting OASIS. This prospective diagnostic study included all primipara women with singleton vaginal delivery at Östersund hospital (Sweden) between 1st Jan 2016 and 31st Jan 2018. The routine postpartum clinical examination with inspection and vaginal and rectal palpation as well as 3D-EAUS recordings were performed directly after delivery. Maternal data were obtained from the medical records. The 3D-EAUS recordings were evaluated by an experienced colorectal surgeon specialized in proctology and 3D-EAUS and compared with the clinical findings. Of the 554 women with satisfactory 3D-EAUS recordings, 23 (4.2 %) had OASIS according to the clinical examination compared to 71 (12.8 %) with the 3D-EAUS. Among the 23 women clinically judged to have OASIS, only 7 could be confirmed with 3-D EAUS. No significant risk factors were found in the group with clinically detected OASIS. Episiotomy was the only risk factor for OASIS seen with 3D-EAUS. OASIS was more frequently detected with 3D-EAUS than with clinical evaluation. Furthermore, only one in three of the clinically observed OASIS cases was confirmed with 3D-EAUS. This indicates that 3D-EAUS is difficult to interpret in an acute obstetric situation and needs further improvement if it is to be a useful tool in detecting OASIS.