Childbirth and incontinence: a prospective study on anal sphincter morphology and function before and early after vaginal delivery

Purpose: Disturbance of anal continence is a well-known problem after vaginal delivery. However, only few and incongruent data on the incidence and pathogenesis of postpartum incontinence are available. This study examined the effects of vaginal delivery on anal continence prospectively. Methods: In 42 unselected women anal vector manometry and endoanal ultrasonography were performed, and pudendal nerve terminal motor latency (PNTML) and rectal sensibility were measured in the 32th week of pregnancy and 6 weeks after delivery. Continence was evaluated according to the Kelly-Holschneider score. Patients with occult sphincter defects were additionally followed-up 12 weeks after vaginal delivery. To exclude any effect of pregnancy alone ten patients with elective cesarian section served as controls. Results: Overall continence after vaginal delivery did not differ significantly from that before delivery, there was a significant reduction in postpartum anal squeeze and resting pressures in all patients. Obstetric tears of grade III or IV occurred in 9% of the patients. Endosonography revealed occult lesions of the internal and external anal sphincter in an additional 19% of women who clinically seemed to have an intact sphincter. Manometric results and continence in these women did not differ significantly from those with intact sphincter and remained unchanged after 12 weeks. PNTML and rectal sensibility were not affected by vaginal delivery. After cesarian section there were no changes in continence, anal pressures, rectal sensibility, or PNTML. Conclusions: Vaginal delivery leads to direct mechanical trauma to the anal sphincters, while stretch and distension of the pudendal nerve seem to be of minor importance. Only endoanal ultrasonography is suitable for detection of occult sphincter lesions.