Could the correct side of mediolateral episiotomy be determined according to anal sphincter EMG?

Introduction and hypothesis Mediolateral episiotomy is one of the most frequent surgical interventions performed in obstetrics. There is conflicting evidence as to whether mediolateral episiotomy reduces the risk of obstetric anal sphincter injuries (OASI). Recent studies suggest that functional asymmetry of pelvic floor innervation exists in healthy women and is strongly associated with postpartum incontinence when the trauma occurs on the dominant side of innervation. Mediolateral episiotomy is the most common cause of perineal trauma during delivery, and the surgical incision is usually performed on the mediolateral right side. Surface electromyography (EMG) has been recently applied in obstetrics for detecting electrical activity of the external anal sphincter (EAS). Methods Two hundred and forty-five pregnant nulliparous women at their second and third trimester of pregnancy were recruited, and EMG signals were detected using a multichannel cylindric anal probe. Measurements were repeated and compared 6–8 weeks after delivery on a subgroup of 167 women who were divided in two groups according to EMG amplitude asymmetry before delivery and two subgroups according to type of delivery: (1A) asymmetric left, episiotomy right; (1B) asymmetric left, other types of deliveries; (2A) asymmetric right, episiotomy right; (2B) asymmetric right, other type of deliveries. Results The reduction of EMG amplitude after right episiotomy was larger in women with right asymmetric sphincter compared with women with left asymmetry and women with other types of delivery. Conclusions Prenatal EMG may be used to predict the impact of right-sided mediolateral episiotomy on EAS and perhaps also function following delivery.