title: Risk factors for obstetric anal sphincter injury: To prolong or to vacuum?
abstract: BACKGROUND
  An awareness of risk factors for obstetric anal sphincter injuries (OASIS) is essential in order to reduce the occurrence of the primary event. These risk factors are demographic, obstetric and intrapartum related. We aimed to identify the risk factors for OASIS and to examine how modifiable risk factors may be used in order to reduce the incidence of OASIS.
  
  
  METHODS
  A retrospective, matched case-control study was conducted in the delivery ward of a single university teaching hospital in Israel, using data from January 2004 to July 2012. All singleton vaginal deliveries at term with OASIS were included. The controls included women matched at a ratio of 1:2 based on gestational age and deliveries that occurred immediately before and after the delivery of the women in the study group.
  
  
  RESULTS
  Overall, 113 OASIS were identified. Stepwise conditional logistic regression revealed that the first vaginal birth (OR = 7.6; 95% confidence interval (CI), 3.5-16.3; p < 0.001) particularly after a previous caesarean section (OR = 13.6; 95% CI, 4.7-39.3; p < 0.001) and the length of the second stage (OR 1.5; 95% CI, 1.1-2.1, p = 0.045) were the only risk factors for OASIS. Among 24 primiparous women who already had a prolonged second stage, 15 delivered by vacuum extraction and nine spontaneously; OASIS occurred in eight (53%) and three (33%) women, respectively. Multivariate analysis showed that this difference was not significant (OR = 2.3; 95% CI, 0.4-12.7; p = 0.35).
  
  
  CONCLUSIONS
  The first vaginal birth particularly after a caesarean delivery and the length of the second stage increased the risk of OASIS. Vacuum extraction performed to shorten a prolonged second stage is not necessarily protective.
authors.affiliation: Rappaport Faculty of Medicine, Technion, Haifa, Israel; Emek Medical Center, Obstetrics and Gynecology, Afula, Israel.
authors.forename: Gali
authors.initials: G
authors.lastname: Garmi
authors.affiliation: Rappaport Faculty of Medicine, Technion, Haifa, Israel.
authors.forename: Hadar
authors.initials: H
authors.lastname: Peretz
authors.affiliation: Emek Medical Center, Obstetrics and Gynecology, Afula, Israel; Emek Medical Center, Urogynecological Unit, Afula, Israel.
authors.forename: Meirav
authors.initials: M
authors.lastname: Braverman
authors.affiliation: Emek Medical Center, Obstetrics and Gynecology, Afula, Israel.
authors.forename: Ilanit
authors.initials: I
authors.lastname: Berkovich
authors.affiliation: Emek Medical Center, Obstetrics and Gynecology, Afula, Israel; Emek Medical Center, Urogynecological Unit, Afula, Israel.
authors.forename: Robert
authors.initials: R
authors.lastname: Molnar
authors.affiliation: Rappaport Faculty of Medicine, Technion, Haifa, Israel; Emek Medical Center, Obstetrics and Gynecology, Afula, Israel. Electronic address: salim_ra@clalit.org.il.
authors.forename: Raed
authors.initials: R
authors.lastname: Salim
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D016022:Case-Control Studies; D036861:Delivery, Obstetric / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007557:Israel / Q000453:epidemiology; D008880:Midwifery; D007744:Obstetric Labor Complications / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors; D014620:Vacuum Extraction, Obstetrical
keywords: Obstetric anal sphincter injuries; Prolonged second stage; Vacuum extraction