title: Perineal body length as a risk factor for ultrasound-diagnosed anal sphincter tear at first delivery.
abstract: OBJECTIVE
  Shortened perineal body (PB) is associated with an increased risk of ultrasound-detected obstetric anal sphincter tear. The objective was to determine if shortened perineal body length (<3 cm) is a risk factor for ultrasound-detected anal sphincter tear at first delivery.
  
  
  METHODS
  Pregnant nulliparous women were recruited over 18 months. At 35-37 weeks' gestation and 6 weeks' postpartum perineal body length (PB) was measured and subjects completed quality of life questionnaires. Primary outcome was ultrasound-diagnosed anal sphincter tear at 6 weeks postpartum. Secondary outcomes were also assessed. A priori power analysis determined that 70 subjects were needed to detect a difference in anal sphincter tear based on a PB cut-off of 3 cm.
  
  
  RESULTS
  Seventy-three subjects completed the study. Mode of delivery was 69.9% spontaneous vaginal, 15.1% operative vaginal, and 15.1% labored cesarean. There were 25 anal sphincter abnormalities (34.2%) seen on ultrasound: 11 (15.1%) internal or external sphincter tears, 3 (4.1%) internal sphincter atrophy, 6 (8.2%) external sphincter thinning, and 7 (9.6%) external sphincter scarring. Only the 11 sphincter tears qualified as abnormal for the primary outcome. In the vaginal delivery group 16.4% (10 out of 61) had a sphincter tear, compared with 8.3% (1 out of 12) in the labored cesarean group (p = 0.68). Women with PB < 3 had a significantly higher rate of ultrasound-diagnosed anal sphincter tear (40.0% vs 11.1%, p = 0.038). When comparing women with and without sphincter tear, there was a significant difference in mean antepartum PB (3.1 vs 3.7 cm, p = 0.043).
  
  
  CONCLUSIONS
  A shortened perineal body length in primiparous women is associated with an increased risk of anal sphincter tear at the time of first delivery.
authors: Division of Female Pelvic Medicine and Reconstructive Surgery, Department of Ob/Gyn, University of North Carolina at Chapel Hill, Chapel Hill, USA, egeller@med.unc.edu.
authors: E J
authors: EJ
authors: Geller
authors: B L
authors: BL
authors: Robinson
authors: C A
authors: CA
authors: Matthews
authors: K P
authors: KP
authors: Celauro
authors: G C
authors: GC
authors: Dunivan
authors: A K
authors: AK
authors: Crane
authors: A R
authors: AR
authors: Ivins
authors: P C
authors: PC
authors: Woodham
authors: J R
authors: JR
authors: Fielding
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D005260:Female; D006801:Humans; D022125:Lacerations / Q000209:etiology*; D007744:Obstetric Labor Complications / Q000209:etiology*; D010298:Parity; D010502:Perineum / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011446:Prospective Studies; D012307:Risk Factors; D014463:Ultrasonography