Disturbed anal sphincter function following vaginal delivery.

BACKGROUND Recently interest in idiopathic (neurogenic) faecal incontinence has swung from denervation of the external anal sphincter to the internal sphincter. AIMS To evaluate the effects of vaginal delivery on the internal sphincter. SUBJECTS 1372 mothers were studied antenatally and 1202 were accepted into the study. METHODS Sphincter pressures were measured antenatally, in the early postnatal period, and six to 10 weeks later in selected patients. RESULTS 755 of 1202 subjects assessed antenatally were primiparous women and 447 multiparous women. Some 320 previous spontaneous vaginal deliveries (SVD) (mean 59 mm Hg) and 67 previous forceps deliveries (mean 58 mm Hg) had lower resting pressures than 755 primiparous women (mean 66 mm Hg) (p < 0.01). A total of 493 subjects were reassessed postnatally. There were 372 SVDs, 47 vacuum extractions, 20 forceps, and 54 caesarean deliveries. All vaginal deliveries but not caesarean sections dropped their resting anal pressures from antenatal values (p < 0.001). Some 227 first SVDs had a much greater fall than 145 subsequent SVDs. In 162 subjects who had undergone their first vaginal delivery and who were followed up there was some recovery but the resting pressures were still lowered at six to 10 weeks post partum. CONCLUSIONS The first vaginal delivery causes a permanent lowering of resting anal pressures. The possible reasons for this are discussed.