Risk factors in childbirth causing damage to the pelvic floor innervation.

The innervation of the pelvic floor musculature is damaged in both stress urinary incontinence and idiopathic (neurogenic) anorectal incontinence. Because childbirth has been considered to be a causative factor in stress incontinence we have assessed the effect of childbirth on the innervation of the pelvic floor musculature in 122 consecutively referred women. They were investigated 48-72 h and 2 months after delivery; 51 were also studied 6 months prior to delivery. In 45 of these 51 women delivered vaginally, EMG studies of the external anal sphincter muscle showed that the fibre density (FD) increased from 1.38 +/- 0.14 before delivery to 1.57 +/- 0.19 2 months after delivery (p less than 0.01). There was no change in the FD in the external anal sphincter muscle after delivery in 20 women delivered by Caesarean section. The pudendal nerve terminal motor latency (PNTML) measured 48-72 h after delivery was increased in the 102 women delivered vaginally compared to 34 nulliparous control subjects. Analysis of the whole group of 122 women showed that multiparity, forceps delivery, increased duration of the second stage of labour, third degree perineal tear and high birth weight were important factors leading to pudendal nerve damage. Epidural anaesthesia had no effect on pudendal nerve function. Modification of these obstetric risk factors may ultimately reduce the frequency of stress urinary and faecal incontinence in women.