title: Is obstetric anal sphincter injury a risk factor for levator ani muscle avulsion in vaginal delivery?
abstract: OBJECTIVE
  To analyze whether women who sustain obstetric anal sphincter injury (OASI) in their first vaginal delivery have a higher incidence of levator ani muscle (LAM) avulsion than do women without OASI.
  
  
  METHODS
  We conducted a prospective observational cohort study of 80 primiparous women who gave birth at our tertiary obstetric unit between September 2011 and July 2013. The women were divided into two groups: women diagnosed with OASI during vaginal delivery (n = 40) and women without OASI (n = 40), matched by mode of delivery and newborn birth weight. Four-dimensional (4D) transperineal ultrasound was performed in all participants at 6-12 months after delivery to assess for integrity or avulsion of the LAM. Ultrasound images were evaluated by two observers who were blinded to group assignment and clinical data. Interobserver agreement was assessed to determine the reproducibility of 4D transperineal ultrasound for diagnosing LAM avulsion.
  
  
  RESULTS
  We found no statistically significant differences between the two groups. The incidence of LAM avulsion was 24.3% in the OASI group and 34.2% in the control group (P = 0.448). Interobserver agreement in the diagnosis of LAM avulsion in the study population using 4D transperineal ultrasound was 89.5%, with a kappa index of 0.76.
  
  
  CONCLUSIONS
  Our findings do not support OASI as a risk factor for LAM avulsion. Prospective studies in larger populations are needed to establish the biomechanical relationships of the pelvic floor structures involved in vaginal delivery. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, Spain.
authors.forename: M Simó
authors.initials: MS
authors.lastname: González
authors.affiliation: Department of Gynecology and Obstetrics, Hospital Universitari Mútua de Terrassa, Terrassa, Spain.
authors.forename: J Cassadó
authors.initials: JC
authors.lastname: Garriga
authors.affiliation: Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, Spain.
authors.forename: C Dosouto
authors.initials: CD
authors.lastname: Capel
authors.affiliation: Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, Spain.
authors.forename: O Porta
authors.initials: OP
authors.lastname: Roda
authors.affiliation: Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, Spain.
authors.forename: J Perelló
authors.initials: JP
authors.lastname: Capó
authors.affiliation: Clinical Epidemiology Unit, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, Spain.
authors.forename: I Gich
authors.initials: IG
authors.lastname: Saladich
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D036861:Delivery, Obstetric / Q000379:methods; D005260:Female; D006801:Humans; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000293:injuries; D015588:Observer Variation; D017773:Pelvic Floor / Q000293:injuries*; D011247:Pregnancy; D011446:Prospective Studies; D012307:Risk Factors; D062606:Tertiary Care Centers; D014463:Ultrasonography / Q000379:methods
keywords: anal sphincter; levator ani muscle; levator ani muscle avulsion; obstetric anal sphincter injury; risk factors; vaginal delivery