Could a mediolateral episiotomy prevent obstetric anal sphincter injury?

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Abstract

Objective

To analyse the significance of risk factors and the role of episiotomy in preventing obstetric anal sphincter injury at vaginal delivery.

Study design

This is a retrospective cross-sectional study in the Norfolk and Norwich University Hospital in the UK. All caesarean sections and non-vertex presentations were excluded, which resulted in a study population of 10,314 deliveries. Obstetric anal sphincter injury (OASI) was defined as third or fourth degree tears to the anal sphincter muscles, with or without a tear involving the anal mucosa. First a univariate analysis was done to identify factors that had a significant association with OASI. Factors included parity, age, gestation, labour induction method, duration of second stage, use of epidural analgesia, episiotomy, method of delivery, time and month of delivery, and birth weight. All factors were then combined in a multivariate logistic regression analysis. The multivariate analysis was then repeated including only factors that had a significant association with OASI in the univariate analysis. Adjusted odds ratios with 95% confidence intervals (CI) were calculated.

Results

The frequency of anal sphincter lacerations was 3.2%. There were statistically significant associations between an increased incidence of OASI and parity, birth weight, method of delivery and shoulder dystocia. Women giving birth without a mediolateral episiotomy were 1.4 times more likely to experience OASI (95% CI 1.021–1.983). Interestingly, the incidence of OASI has risen between 2005 and 2007.

Conclusion

Parity, age, birth weight, method of delivery and shoulder dystocia are strongly associated with obstetric anal sphincter injury. Mediolateral episiotomy appears to be protective against OASI but a randomised controlled trial would be needed to confirm this. The rising incidence of OASI after normal vaginal deliveries may be related to adoption of the hands off technique or increased identification of tears.

Introduction

Anal incontinence is believed to affect nearly 40,000 mothers annually in the UK [1], [2], [3], [4]. Traumatic vaginal delivery is the major cause of faecal incontinence in women [5], [6], and studies using endo-anal ultrasonography have shown that faecal incontinence is caused by sphincter damage [7], [8]. Episiotomy, as the most commonly performed obstetric operation, has been a routine part of instrumental deliveries with the aim of decreasing the risk of obstetric anal sphincter injury (OASI). Two mechanisms of injury are generally recognised: direct disruption of the anal sphincter muscles and traction neuropathy affecting the pudendal nerves [9]. Even in women with overt tears diagnosed and repaired at birth, the outcome is often unfavourable [8], [10], [11]. About 30–50% of these women suffer from chronic anal incontinence, dyspareunia, faecal urgency or perineal pain [8], [10], [12], [13]. The reported incidence of third degree tears varies between 0.5% and 6% of vaginal deliveries in centres where mediolateral episiotomy is practised [5], [7], [8], [12], [14], [15], [16].

A first report of episiotomy goes far back to 1741, when Ould described this as surgical opening of the perineum to prevent severe perineal tears [17], but there now appears to be a trend towards a decrease in the use of episiotomy. The objective of this study was to analyse the risk factors of OASI with special reference to the effect of mediolateral episiotomy on OASI.

Section snippets

Materials and methods

This was a retrospective cross-sectional study based at the Norfolk and Norwich University Hospital in the UK. OASI was defined as any injury to the anal sphincter muscles, with or without a tear involving the anal mucosa. Data for the statistical analysis were obtained from the maternity database at the hospital. This database contains all available information recorded after each delivery. A printed output from this database is used in case notes as a record of delivery. The existing hospital

Results

All caesarean sections, non-vertex presentations and incomplete data were excluded from the study, resulting in a study population of 10,314 deliveries. Descriptive statistics for the subjects are shown in Table 1, and statistics for the birth are shown in Table 2. 1666 subjects (16.2%) had an episiotomy. 332 of 10,314 subjects (3.2%) had third and fourth degree perineal tears. 58% of OASI were sustained after normal vaginal delivery (NVD), 22% after forceps delivery and 20% after ventouse

Conflict of interests

None to declare.

Funding

None to declare.

Acknowledgement

We thank Alice Walmesley of Dianthus Medical Limited for editing assistance.

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