title: Risk factors for anal sphincter tears: the importance of maternal position at birth.
abstract: OBJECTIVE
  To assess the role of birth position in the occurrence of anal sphincter tears (AST).
  
  
  METHODS
  Observational cohort study.
  
  
  METHODS
  South Hospital in Stockholm, a teaching hospital with around 5700 births per year.
  
  
  METHODS
  Among all 19,151 women who gave birth at the South Hospital during the study period 2002-05, 12,782 women met the inclusion criteria of noninstrumental, vaginal deliveries.
  
  
  METHODS
  Data on birth position and other obstetric factors were analysed in relation to occurrence of AST.
  
  
  METHODS
  Third- and fourth-degree AST.
  
  
  RESULTS
  AST occurred in 449 women (3.5%). The trauma was more frequent in primiparous (5.8%) than in multiparous women (1.7%). The highest proportion of AST was found among women who gave birth in lithotomy position (6.9%), followed by squatting position (6.4%). Logistic regression analyses showed that lithotomy (adjusted OR 2.02, 95% CI 1.58-2.59) and squatting positions (adjusted OR 2.05, 95% CI 1.09-3.82) were associated with a significantly increased risk for AST. Other major risk factors for anal sphincter trauma were primiparity (adjusted OR 3.29, 95% CI 2.55-4.25), prolonged second stage of labour >1 hour (adjusted OR 1.52, 95% CI 1.11-2.10), infant birthweight more than 4 kg (adjusted OR 2.12, 95% CI 1.64-2.72) and large infant head circumference (adjusted OR 1.57, 95% CI 1.23-1.99).
  
  
  CONCLUSIONS
  Lithotomy and squatting position at birth were associated with an increased risk for AST also after control for other risk factors.
authors: Department of Women and Child Health, Division of Reproductive and Perinatal Health, Karolinska Institutet, Stockholm, Sweden. karin.gottvall@ki.se
authors: K
authors: K
authors: Gottvall
authors: P
authors: P
authors: Allebeck
authors: C
authors: C
authors: Ekéus
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D001724:Birth Weight; D005260:Female; D006801:Humans; D022125:Lacerations / Q000209:etiology; D015999:Multivariate Analysis; D007744:Obstetric Labor Complications / Q000209:etiology*; D016017:Odds Ratio; D010298:Parity; D011187:Posture / Q000502:physiology*; D011247:Pregnancy; D012307:Risk Factors