Perineal body length as a risk factor for ultrasound-diagnosed anal sphincter tear at first delivery

E. J. Geller, B. L. Robinson, C. A. Matthews, K. P. Celauro, G. C. Dunivan, A. K. Crane, A. R. Ivins, P. C. Woodham, J. R. Fielding

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Introduction and hypothesis: 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 post-partum. 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.

Original languageEnglish (US)
Pages (from-to)631-636
Number of pages6
JournalInternational Urogynecology Journal and Pelvic Floor Dysfunction
Issue number5
StatePublished - May 2014
Externally publishedYes


  • Endoanal ultrasound
  • Obstetric anal sphincter tear
  • Perineal body
  • Primiparous
  • Risk factors

ASJC Scopus subject areas

  • Obstetrics and Gynecology
  • Urology


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