title: Trigonometric characteristics of episiotomy and risks for obstetric anal sphincter injuries in operative vaginal delivery.
abstract: OBJECTIVE
  The objective of this study was to investigate the association between the trigonometric properties of episiotomy in operative vaginal delivery (OVD) and obstetric anal sphincter injuries (OASIS).
  
  
  METHODS
  The study included 72 primiparous women who had an OVD and episiotomy. Cases (n = 36) had sustained OASIS at birth, while controls (n = 36) had not. The groups were matched for instrumental delivery. The episiotomy scar was identified and its trigonometric characteristics were measured at 8-12 weeks postpartum. Data were analysed using conditional logistic analysis.
  
  
  RESULTS
  The angle of episiotomy behaves as a factor associated with anal sphincter injury, so women with a mediolateral episiotomy and an angle greater than 20° have an 87% less risk of having an OASIS (odds ratio 0.13, 95% confidence interval 0.03-0.58). The study showed that scarred episiotomies at 8-12 weeks after OVD with an angle ≤ 20°, depth and distance between the episiotomy and anus ≤ 15 mm, total upper triangle perimeter ≤ 75 mm, para-anal triangle perimeter ≤ 15 mm and areas between scar and midline ≤ 250 mm(2) were significantly associated with higher risk of OASIS.
  
  
  CONCLUSIONS
  When a mediolateral episiotomy is performed in OVD the technique has a strong effect on the occurrence of OASIS. Additional research is needed to determine if the optimal technique for mediolateral episiotomies produces less OASIS than deferring the performance of episiotomy.
authors.affiliation: Pelvic Floor Unit, Department of Obstetrics and Gynaecology, Complejo Asistencial Universitario of León (CAULE), C/ Altos de Nava S/N, 24080, León, Spain, enriquegonzalezdiaz@hotmail.com.
authors.forename: E
authors.initials: E
authors.lastname: Gonzalez-Díaz
authors.forename: L
authors.initials: L
authors.lastname: Moreno Cea
authors.forename: A
authors.initials: A
authors.lastname: Fernández Corona
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D002921:Cicatrix / Q000209:etiology / Q000473:pathology; D004841:Episiotomy / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006801:Humans; D022125:Lacerations / Q000209:etiology*; D055641:Mathematical Concepts; D007744:Obstetric Labor Complications / Q000209:etiology*; D011247:Pregnancy; D012307:Risk Factors; D015599:Trauma Severity Indices