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Objectives To assess risk factors and outcome of different grades of obstetric anal sphincter injuries (OASIS) after primary repair, and to assess the relationship between outcome of anal sphincter defects as diagnosed by endoanal ultrasound.

Methods We included 531 consecutive women (of which eight were tertiary referrals) who had sustained OASIS, underwent primary sphincter repair and were followed up between July 2002 and July 2008. At follow-up, defecatory symptoms and bowel-related quality of life (QoL) were evaluated and anal manometry and endoanal ultrasound were performed.

Results The mean time of follow-up was 9 (SD, 5.9) weeks after delivery. Compared with women with a minor (Grade 3a/3b) tear, those with a major (Grade 3c/4) one had a significantly poorer outcome (P < 0.05) with respect to the development of defecatory symptoms and associated QoL as well as anal manometry. Women with major tears were significantly more likely to have an endosonographic isolated internal anal sphincter (IAS) or combined IAS and external anal sphincter (EAS) defect. Combined defects were associated with a higher risk of loose fecal incontinence and lower anal canal pressures. Use of epidural analgesia was the only independent factor predicting a major tear.

Conclusions The greater likelihood of endosonographic anal sphincter defects in women with major tears compared with minor tears is the probable cause of the less favorable outcome of primary repair. Endosonographic combined defects are associated with poorer outcome and it is therefore important to identify the full extent of injury at delivery in women who sustain OASIS, and to pay particular attention to repair of IAS defects. Copyright (C) 2010 ISUOG. Published by John Wiley & Sons, Ltd.