Impact of Delivery on the Anal Sphincter Innervation

Recent studies demonstrated that there is a significant correlation between external anal sphincter (EAS) damage during vaginal birth and subsequent development of anal incontinence. Functional asymmetry of pelvic floor innervation has been observed. A new non-invasive method-surface electromyography (sEMG)-has been shown to be useful to detect the innervation pattern of EAS. Data from 33 primiparous women with subsequent episiotomy at labour were analysed. sEMG measurements were performed with a disposable rectal probe at the 28th to 34th gestational week and 6-8 weeks after delivery. The innervation zones (IZs) of single motor unit were identified by means of a recently developed signal processing technique. Women were divided into three groups according to the distribution of innervation zones pre-partum: innervated predominantly left, symmetric or predominantly right. In women with a prevalence of innervation zones on the right, a statistically significant reduction of the number of IZs was observed after delivery (Wilcoxon signed-rank test, p = 0.0156), while predominantly left or symmetric innervated women did not show any changes in their innervation pattern. If the episiotomy is performed on the predominantly innervated side of the sphincter, it causes a significant damage to the innervation.