Quantitative electromyography of the anal sphincter after uncomplicated vaginal delivery

OBJECTIVE: Fecal incontinence in women is thought to be associated with sphincter laceration or pudendal nerve damage. A prolonged pudendal nerve terminal motor latency is evidence of profound nerve damage, but pudendal nerve terminal motor latency can be normal even when nerve injury has been sustained. We performed quantitative electromyography (EMG) to compare multiple motor unit action potential parameters between recently postpartum women and nulliparous women. METHODS: Standardized examinations were prospectively performed on 2 groups: 1) healthy nulliparous women without pelvic floor disorders (n = 28) and 2) asymptomatic women who were postpartum following vaginal delivery of their first child (n = 23). The examinations included pelvic organ prolapse quantification measurements, endoanal ultrasonography, pudendal nerve terminal motor latency, sacral reflexes, and concentric needle EMG using multiple motor unit action potential analysis. RESULTS: A mean of 11.5 (standard deviation [SD] 1.1) weeks had elapsed since first vaginal deliveries in the postpartum group. The mean fetal weight at delivery was 3,495 (SD 458) grams. There were no sphincter defects seen by ultrasonography. Compared with the nulliparous women, pudendal nerve terminal motor latency and sacral reflexes (clitoral-anal reflex, urethral-anal reflex) were not increased in the postpartum group. Each of the quantitative parameters (duration, amplitude, area, turns, and phases), measured from motor unit action potentials in the postpartum group, were larger than in the nulliparous group (P ≤ .004, nested analysis of variance [ANOVA]). CONCLUSION: Quantitative EMG using multiple motor unit action potential analysis can detect the presence after vaginal childbirth of subtle nerve injury not demonstrable by pudendal nerve terminal motor latency. Even asymptomatic women show evidence of pelvic floor nerve injury after uncomplicated deliveries.