[Effect of delivery on the anal sphincter]

SPHINCTER TEARS: Vaginal delivery can lead to tears in the anal sphincters. Total perineal distension following expulsion concerns less than 1% of all deliveries. Initially, sphincter tears generally go unnoticed although echographically detectable defects can be found in one-third of all primiparturients. The inner or outer sphincter may be involved alone or in combination as is seen in half of the cases.

Moderate signs of incontinence (gas, urge) are frequently reversible although the long-term outcome remains unknown. In half of the cases, perineal denervation is secondary to stretch lesions of the pudendal nerve terminasions.

Primiparity, forceps delivery, fetal macrosomy, and certain presentations (breech, occipitoposterior) may favor sphincter lesions.

A complete examination of the posterior perineum is required with anorectal manometry, a perineal electrophysiologic study, and a transanal ultrasound study whenever function signs are found at the post partum follow-up.

The therapeutic strategy is guided by the exploration results. In case of symptomatic rupture of the external sphincter, sphicteroplasty is needed followed by functional rehabilitation therapy with biofeedback. Women who have suffered traumatic lesions of the posterior perineum should be carefully followed for signs of secondary incontinence. Cesarean section may be indicated as a preventive measure in case of a new pregnancy.