Sphincter muscle activity before and after delivery: Does it depend on the type of birth?

AIM: There are ongoing discussions whether cesarean section is the safest mode of childbirth to prevent pelvic floor disorders. Pelvic floor electromyography (EMG) allows the analysis of external anal sphincter (EAS) function during voluntary contractions. The primary objective of this study was the evaluation of EMG amplitude of external anal sphincter in women who had vaginal delivery, compared to women who had cesarean section. The secondary objective was to evaluate the anal incontinence score changes before and after delivery between the groups, and to look for any relationship between the clinical and EMG findings. METHODS: Multichannel surface EMG was detected during maximal contractions in three sessions: (i) during pregnancy, (ii) 6 weeks after delivery and (iii) 1 year after delivery. Women were divided into two groups: cesarean section and vaginal delivery. RESULTS: External anal sphincter EMG amplitude decreases 6 weeks after vaginal deliveries from 10.1 to 8.6 µV with effect size of 0.4, but returns to baseline after 1 year. No differences were observed between groups in all other variables. CONCLUSION: No differences were observed after 1 year in EMG activity between the two groups; however, a slight decrease of sphincter muscle amplitude was noted 6 weeks after vaginal delivery. The delivery mode does not have effect on the EAS amplitude 1 year after delivery. Incontinence score slightly increased in both groups after delivery, with no significant differences between the two groups. No association was observed between the increase of incontinence score and the decrease of EMG signal amplitude.

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.

Impact of mediolateral episiotomy on incidence of obstetrical anal sphincter injury diagnosed by endoanal ultrasound.

OBJECTIVE: to examine potential association between mediolateral episiotomy and reduced incidence of obstetrical anal sphincter injuries (OASIS) diagnosed by endoanal ultrasound. DESIGN: prospective cohort study. SETTING: tertiary referral university hospital. PARTICIPANTS: sixty nulliparous women at 28-33 weeks of gestation with singleton pregnancies were included between 2010 and 2012. MEASUREMENTS AND FINDINGS: participants were examined with endoanal ultrasound at 28-33 weeks gestation and at 6-7 weeks post-partum. At both visits, symptoms of anal incontinence were assessed using Cleveland Clinic (Wexner) faecal incontinence scoring system. Mann Whitney U-test and χ2 test was used to compare groups with vs. without episiotomy and groups with vs. without OASIS diagnosed by ultrasound. χ2 test was used to assess correlation between OASIS and anal incontinence symptoms (p≤0.05 considered significant). None of the women included had sphincter injury or anal incontinence before childbirth. All delivered vaginally. Mediolateral episiotomy was performed in 33 (55%) cases. Six (10%) had OASIS on endoanal ultrasound (two were also diagnosed clinically), and 11 had symptoms of anal incontinence post-partum. No significant differences were seen in clinical characteristics between groups with vs. without episiotomy. No significant differences were seen in episiotomy rate (p=0.14), angle (p=0.42) and length (p=0.14) between groups with vs. without OASIS on ultrasound. Correlation between anal incontinence symptoms and sonographically diagnosed OASIS was statistically significant (p=0.04). KEY CONCLUSIONS: mediolateral episiotomy does not seem to be protective against clinically or sonographically diagnosed OASIS even when episiotomy technique is considered. Endoanal ultrasound allows a significantly better detection of symptomatic OASIS compared to clinical examination alone. IMPLICATIONS FOR PRACTICE: mediolateral episiotomy should be considered only when shortening the second stage of labour is indicated due to foetal distress, and not as a means of OASIS prevention.

Effect of vaginal delivery on the external anal sphincter muscle innervation pattern evaluated by multichannel surface EMG: results of the multicentre study TASI-2.

INTRODUCTION AND HYPOTHESIS: A correlation exists between external anal sphincter (EAS) damage during birth and the subsequent development of fecal incontinence. This study evaluated the effect of delivery-related trauma on EAS innervation by means of intra-anal EMG performed with a rectal probe with 16 silver electrodes equally spaced along the circumference, before and after delivery. METHODS: Pre-partum EMG measurements were performed on 511 women, by nine clinical partners from five European countries at the 28th to 34th gestational weeks and the 6th to 8th post-delivery weeks; 331 women returned, after delivery, for the second test. The innervation zones (IZ) of EAS single motor units were identified by means of an EMG decomposition algorithm. RESULTS: The subjects were divided into four groups according to the delivery mode (Caesarean, vaginal with no evident damage, spontaneous lacerations and episiotomies). The number of IZs before and after delivery was compared. In the 82 women who underwent right mediolateral episiotomy, a statistically significant reduction of IZs was observed, after delivery, in the right ventral quadrant of the EAS (side of the episiotomy). Women who had Caesarean section, spontaneous lacerations or lack of evident damage did not present any significant change in the innervation pattern. CONCLUSIONS: Right episiotomy reduces the number of IZs on the right-ventral side of the EAS. The fast and reliable test proposed indicates the sphincter innervation pattern before delivery and helps obstetricians to evaluate the risks and to choose the preferred side of the episiotomy, if deemed necessary at the time of delivery.

Characterization of the motor units of the external anal sphincter in pregnant women with multichannel surface EMG.

INTRODUCTION AND HYPOTHESIS: Locating the innervation zones (IZs) of the external anal sphincter (EAS) is helpful to obstetricians to identify areas particularly vulnerable to episiotomy in pregnant women. The aim was to investigate the motor unit (MU) properties of the EAS during voluntary contractions. METHODS: Electromyographic signals were detected, from 478 pregnant women, by means of an intra-anal cylindrical probe carrying a circumferential array of 16 electrodes. The signals were decomposed into the constituent MU action potential trains and 5,947 templates were extracted and analyzed in order to identify the IZ position. RESULTS: MUs innervated at one end are concentrated in the dorsal portion of the sphincter, while MUs innervated in the middle are distributed symmetrically in the left and right portions of the EAS. The angular propagation velocity was estimated for each MU resulting in 260 ± 45 rad/s, corresponding to 1.8 m/s on the probe surface and to about 4 m/s at a radial depth of 10 mm from the probe surface. CONCLUSIONS: A novel method for identification and classification of MUs of the EAS is proposed and applied to a large-scale study. It is possible to distinguish MUs of the EAS in a minimally invasive way and identify their IZs. This information should be used to plan episiotomies and minimize risks of EAS denervation.