Perineal tears are more likely to occur with:
- precipitant labour
- shoulder dystocia
- with forceps deliveries
- narrow suprapubic arch
- big babies
- babies with poorly flexed heads
Perineal injury remains the commonest form of maternal obstetric injury and had been traditionally classified into first, second and third degree (in the UK, a third degree tear used to be recorded only if the anal sphincter was completely disrupted and the rectal mucosa was breached. In the USA, a tear that involved the anal sphincter to any degree was classified as third degree, and one that involved the rectal mucosa was called fourth degree). The classification used in the UK has been updated and now distinguishes first, second, third and fourth degree tears (1):
- First degree tear - tear involving the perineal or vaginal skin only
- Second degree tear - perineal skin and muscles torn, but intact anal sphincter
- Third degree perineal tear - perineal skin, muscles and anal sphincter are torn
- a. Less than 50% of the external anal sphincter thickness is torn
- b. More than 50% of the external anal sphincter thickness is torn, but internal anal sphincter intact
- c. Both external and internal anal sphincters are torn, but anal mucosa intact
- Fourth degree perineal tear - perineal skin, muscles, anal sphincter and anal mucosa are torn
- Button-hole tear - anal sphincter is intact but anal mucosa is torn
Anatomically an episiotomy involves the same structures as a second degree perineal tear
Management depends on the type of tear:
General principles for management are:
- labial tear - uncomfortable; heal quickly; rarely require suturing
- first degree tear - superficial; no involvement of muscle; may not require suturing if there is only minimal blood loss
- second degree tear - involve perineal muscle require suturing
- third and fourth degree tears - requires repair by an experienced surgeon
Notes:
- a systematic review (2) noted that limited data available showed that, compared to immediate primary end-to-end repair of obsetric anal sphincter injuries, early primary overlap repair appeared to be associated with lower risks for faecal urgency and anal incontinence symptoms. However the review noted that experience of the surgeon was not addressed in the studies reviewed, and therefore it would be inappropriate to recommend one type of repair in favour of another
- in the majority of cases either a first or second degree tear is sustained - serious sequelae are infrequent
- anal sphincter tears are a relatively uncommon occurrence on any delivery suite
- reported incidence varies considerably but it is usually between 0.5% and 2.5% of vaginal deliveries
- anal sphincter tears are an important risk factor for long-term anal sphincter dysfunction
- up to 60% of women who sustain a sphincter tear are reported to experience symptoms of dyspareunia, perineal pain or anal incontinence
Reference:
- Fernando RJ, Sultan AH. Risk factors and management of obstetric perineal injury. Curr. Obs. & Gynae. 2004; 14 (5):320-326.
- Fernando R et al. Methods of repair for obstetric anal sphincter injury. Cochrane Database Syst Rev. 2006 Jul 19;3:CD002866
- Byrd LM et al. Is it possible to predict or prevent third degree tears? Colorectal Dis. 2005 Jul;7(4):311-8.