title: Risk factors associated with anal sphincter tear: a comparison of primiparous patients, vaginal births after cesarean deliveries, and patients with previous vaginal delivery.
abstract: OBJECTIVE
  This study was conducted to identify obstetric risk factors for anal sphincter tear in primiparous patients, patients with a previous cesarean delivery (VBAC), and patients with a previous vaginal delivery (PVD).
  
  
  METHODS
  An obstetrics automated record system was accessed to retrospectively review records of all singleton vaginal deliveries at greater than 36 weeks' gestation (excluding breech and stillbirth) from 1995 through 2000 (n = 10,928). A number of potential risk factors for anal sphincter tear (third- and fourth-degree episiotomy extensions and lacerations) were tested with use of multivariate logistic regression analysis.
  
  
  RESULTS
  The risk of anal sphincter tear was significantly increased with primiparity (relative risk [RR] 4.08) and VBAC (RR 5.46) compared with PVD, birth weight greater than 4000 g (RR 2.41), forceps delivery (RR 6.00), vacuum delivery (RR 2.18), shoulder dystocia (RR 3.28), and episiotomy (RR 2.59).
  
  
  CONCLUSIONS
  Efforts to prevent anal sphincter tear might include reconsideration of modifiable risk factors such as episiotomy, operative vaginal delivery, and VBAC.
authors.affiliation: Division of Medical and Surgical Gynecology, Department of Obstetrics and Gynecology, University of Alabama at Birmingham, 35249-7333, USA.
authors.forename: Holly E
authors.initials: HE
authors.lastname: Richter
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Brumfield
authors.forename: Suzanne P
authors.initials: SP
authors.lastname: Cliver
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Burgio
authors.forename: Cherry L
authors.initials: CL
authors.lastname: Neely
authors.forename: R Edward
authors.initials: RE
authors.lastname: Varner
mesh_terms: D000328:Adult; D001741:Black or African American; D001003:Anal Canal / Q000293:injuries*; D036861:Delivery, Obstetric; D005260:Female; D006801:Humans; D008499:Medical Records; D009772:Obstetrical Forceps / Q000009:adverse effects; D010298:Parity; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors; D012421:Rupture / Q000208:ethnology / Q000209:etiology; D016064:Vaginal Birth after Cesarean; D044465:White People