Objective To investigate changes in anal canal anatomy following vaginal de
livery in women without apparent sphincter injury. Prospective controlled o
bservational study. Design
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 subje
cts 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 def
ined 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 (m
ean 3.7 mm vs 4.6 mm, P < 0.01) in association with lateral external sphinc
ter thickening (mean 7.0 mm vs 4.4 mm, P < 0.01), and longitudinal muscle t
hickening (mean 2.8 mm vs 2.1 mm, P < 0.01).
Conclusions Specific changes in anal morphology have been demonstrated foll
owing vaginal delivery in women without apparent sphincter injury.