Obstetric anal sphincter injuries: review of anatomical factors and modifiable second stage interventions

Introduction and hypothesis: Obstetric anal sphincter injuries (OASIs) are the leading cause of anal incontinence in women. Modification of various risk factors and anatomical considerations have been reported to reduce the rate of OASI. Methods: A PubMed search (1989 – 2014) of studies and systematic reviews on risk factors for OASI. Results: Perineal distension (stretching) of 170% in the transverse direction and 40% in the vertical direction occurs at crowning, leading to significant differences (15 – 30 °) between episiotomy incision angles and suture angles. Episiotomies incised at 60 ° achieve suture angle…