Obstetric Anal Sphincter Injuries (OASI) represent severe perineal tears involving at least a partial rupture of the external anal sphincter which occurs for 0.4-5% of deliveries and could strongly impact women’s health. It corresponds to stage 3 or more of the Royal College of Obstetricians and Gynaecologists (RCOG) classification. Several risk factors are well described in the literature such as: nulliparity, short perineal body, increased fetal weight, posterior fetal presentation, prolonged second stage of labor, medial episiotomy and instrumental delivery [1]. It is also well reported that a liberal use of a mediolateral episiotomy in vaginal delivery has no benefit in order to avoid an OASI. Nevertheless, the potential protective effect of mediolateral episiotomy during instrumental vaginal delivery remains unclear. Instrumental delivery is a high-risk situation for OASI occurrence, especially when other risk factors co exists (posterior presentation, nulliparity). The literature in this thematic is contradictory but there are several studies reporting an increase in OASI occurrence when there is an instrumental delivery without episiotomy [2]. These studies are difficult to interpret since they often deal with teams having a liberal use of episiotomy. This considered it remains unclear if a restrictive use of mediolateral episiotomy during an instrumental delivery is associated with a higher risk of OASI.

Since 2005, according to the French guidelines, our institution introduced a restrictive use of mediolateral episiotomy for all vaginal deliveries including instrumental deliveries. We hypothesize that this change in our practices may have been affect our OASI incidence.

The main endpoint of this study was to assess if there is an increased risk of OASI associated with a restrictive use of mediolateral episiotomy during instrumental delivery.

This is a retrospective study based on a French university maternity register. We collected and entered into the register at the time of birth data about women characteristics (age, body mass index, parity), mode of delivery: epidural analgesia, term, second stage of labor length, expulsive phase length, mediolateral episiotomy use and type of instrument used, OASI occurrence with the RCOG classification and birthweight. We analyzed all the instrumental deliveries at more than 34 weeks of gestation for singleton in cephalic presentation between January 2005 and December 2015.
Continuous variables were compared using a Student t test and categorical variables were compared using a χ2 test. We performed a multivariate analysis using a logistic regression in order to investigate the effect of mediolateral episiotomy during an instrumental delivery for OASI occurrence. For all analyses, significance was considered for p<0.05 and we calculated Odd Ratios (OR) with 95% confidence interval when it was appropriate. When admitted in our institution, each patient receive the hospital chart that specifically mentions the possibility that anonymized medical data collected during hospitalization could be used for medical research. Considering French regulations, ethical committee approval was not required for this retrospective study.

Among 19792 vaginal deliveries of singleton in cephalic presentation upon 34 weeks of gestation, 2357 were instrumental deliveries (11.9%). These 2357 instrumental deliveries were associated with a mediolateral episiotomy in 950 cases (40.3%) and an OASI occurred in 174 cases (7.4%). Characteristics of women and mode of delivery are reported in table 1. Between 2005 and 2015, we observed a significant reduction of our rate of episiotomy for instrumental delivery from 78.5 to 16.2% (p<0.05) whereas our rate of OASI increased from 3.1 to 12.7% (p<0.05) (Figure 1). We found an OR at 3.66 [2.5-5.5] for OASI occurrence in case of instrumental delivery without  episiotomy.

In our experience a restrictive use of mediolateral episiotomy for instrumental delivery was associated with an increase of OASI occurrence in a 11-year period.
The main strength of this study is that it provides data about the effect of episiotomy in instrumental delivery in a team with a restrictive use of episiotomy whereas most of the papers available came from teams with a liberal use of episiotomy. The main limitation is that it was a retrospective and mono centric study. This considered, our study is not able to demonstrate the protective effect of mediolateral episiotomy in instrumental delivery. The increase of OASI incidence that we reported may have two origins. The first one is a potential protective effect of episiotomy in this specific indication and the second is that since 2010 our team implement a standardized description of OASI using the RCOG classification whereas before 2010 we used the French classification. This might have  induced more diagnosis of OASI with tears that would not have been classed as OASI with the French classification (especially stage 3A). Finally, the potential protective effect of episiotomy might be interesting in cases where multiple risk factors exist (nulliparous, posterior presentation, forceps) with a very high risk of OASI. In such conditions, the use of mediolateral episiotomy should be considered to avoid OASI.

A restrictive use of episiotomy during instrumental delivery seems associated with an increased risk of OASI. Mediolateral episiotomy should be considered when instrumental delivery is associated with several risk factors for OASI

Gynecol Fertil Obstet Senol. 2018. DOI:10.1016/j.gofs.2018.01.004
Int Urogynecol J. 2018. DOI:10/1017/s00192-017-3422-4