Anal sphincter electromyography after vaginal delivery: neuropathic insufficiency or normal wear and tear?

The study was performed to evaluate the potential role of vaginal delivery on innervation of the external anal sphincter (EAS) muscle. Forty-four women, 18 nulliparous and 26 of varying parity (1-4), without genitourinary prolapse, major urogynecological, anorectal, or neurological dysfunction were included. Participants' histories were evaluated by a questionnaire. Quantitative concentric needle electromyography (EMG) using multi-MUP analysis for sampling motor unit potentials (MUPs) in all volunteers, and "turn/amplitude" analysis for interference pattern (IP) analysis in 13 nulliparous and 23 parous women were applied. Pools of MUPs and IPs of parous and nulliparous women were formed and compared using the Mann-Whitney U test. Multiple linear regression analysis was used for evaluation of parity and obstetric variables. No difference between the groups was found in any MUP parameter, while a significant difference was found in two of five IP parameters. On multiple linear regression analysis, the number of deliveries was related to several MUP and IP parameters: the time elapsed since last delivery to MUP, and slight stress urinary incontinence to IP parameters. A group of parous women with (slight) stress incontinence had less "pathologic" MUP parameters, compared to those without. Vaginal delivery is indeed related to EAS muscle EMG abnormalities. However, these are minor and seem not to indicate loss of sphincter function. Our study casts some doubt on the commonly accepted preconception that significant damage to peripheral innervation of the EAS occurs even during uncomplicated deliveries.