Changes in anal anatomy following vaginal delivery revealed by anal endosonography

OBJECTIVE: To investigate changes in anal canal anatomy following vaginal delivery in women without apparent sphincter injury. DESIGN: Prospective controlled observational study. SETTING: District general hospital. POPULATION: Consecutive parous and nulliparous women attending a gynaecology outpatient clinic. METHODS: All women were examined using anal endosonography, and parous subjects without apparent sphincter injury compared with age-matched nulliparous controls to determine any differences in general anal canal morphology. MAIN OUTCOME MEASURES: Individual anal canal components were measured at defined levels and subjects compared with controls. RESULTS: Twenty-one of 54 parous women had no anal sphincter scar. Compared with nulliparous women, they had significant anterior sphincter thinning (mean 3.7 mm vs 4.6 mm, P< 0.01) in association with lateral external sphincter thickening (mean 7.0 mm vs 4.4 mm, P<0.01), and longitudinal muscle thickening (mean 2.8 mm vs 2.1 mm, P< 001). CONCLUSIONS: Specific changes in anal morphology have been demonstrated following vaginal delivery in women without apparent sphincter injury.