Anal canal pressures are low in women with postpartum anal fissure

Anal sphincter hypertenia is commonly thought to underlie development of anal fissure, yet anal fissure is particularly common after childbirth, a time when anal canal pressure may be reduced. This paradox was investigated by a prospective study of the effect of parturition on the pelvic floor.

Anal manometry was performed 6 weeks before and after delivery in 209 primigravid women with no pre-existing history of anorectal disease. Postpartum studies only were performed on a further 104 primiparae. Anal fissure was diagnosed by history and direct examination.

Some 29 women (9 per cent) developed postpartum anal fissure. Antepartum anal canal resting and squeeze pressures were similar in women who did and those who did not develop fissure. Resting and squeeze anal canal pressures decreased post partum in both groups. Postpartum constipation was more common in those with fissure (62 per cent) than in those without (29 per cent) (chi 2 = 10.6, 1 d.f., P < 0.01). The mode of delivery or use of epidural analgesia did not affect the incidence of fissure.

Postpartum anal fissure is associated with reduced anal canal pressures, and surgical interference with the anal sphincter mechanism should be avoided.