title: Anal sphincter tears: prospective study of obstetric risk factors.
abstract: OBJECTIVE
  To evaluate intrapartum risk factors for anal sphincter tear.
  
  
  METHODS
  A prospective observational study.
  
  
  METHODS
  Delivery unit at the University Hospital in Göteborg, Sweden.
  
  
  METHODS
  2883 consecutive women delivered vaginally during the period between 1995 and 1997. Information was obtained, from patient records and from especially designed protocols which were completed during and after childbirth.
  
  
  METHODS
  Anal sphincter (third and fourth degree) tear.
  
  
  RESULTS
  Anal sphincter tear occurred in 95 of 2883 women (3.3%). Univariate analysis demonstrated that the risk of anal sphincter tear was increased by nulliparity, high infant weight, lack of manual perineal protection, deficient visualisation of perineum, severe perineal oedema, long duration of delivery and especially protracted second phase and bear down, use of oxytocin, episiotomy, vacuum extraction and epidural anaesthesia. After analysis with stepwise logistic regression, reported as odds ratio, 95% confidence interval, the following factors remained independently associated with anal sphincter tear: slight perineal oedema (0.40, 0.26-0.64); manual perineal protection (0.49, 0.28-0.86); short duration of bear down (0.47, 0.24-0.91); no visualisation of perineum (2.77, 1.36-5.63); parity (0.59, 0.40-0.89); and high infant weight (2.02, 1.30-3.16). Analysis of variance showed that manual perineal protection had a stronger influence on lowering the frequency, and lack of visualisation of perineum and infant weight had a stronger influence on raising the frequency, of anal sphincter tears in nulliparous compared with parous women.
  
  
  CONCLUSIONS
  Perineal oedema, poor ocular surveillance of perineum, deficient perineal protection during delivery, protracted final phase of the second stage, parity and high infant weight all constitute independent risk factors for anal sphincter tear. Such information is essential in order to reduce perineal trauma during childbirth.
authors.affiliation: Perinatal Center, Department of Obstetrics and Gynaecology, Sahlgrenska University Hospital/Ostra, Göteborg, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Samuelsson
authors.forename: L
authors.initials: L
authors.lastname: Ladfors
authors.forename: U B
authors.initials: UB
authors.lastname: Wennerholm
authors.forename: B
authors.initials: B
authors.lastname: Gåreberg
authors.forename: K
authors.initials: K
authors.lastname: Nyberg
authors.forename: H
authors.initials: H
authors.lastname: Hagberg
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D000704:Analysis of Variance; D001724:Birth Weight; D005260:Female; D005865:Gestational Age; D006801:Humans; D007744:Obstetric Labor Complications / Q000517:prevention & control*; D010298:Parity; D011247:Pregnancy; D011295:Prenatal Care / Q000379:methods*; D011446:Prospective Studies; D012307:Risk Factors; D012421:Rupture