Perineal trauma (damage to the area between the vaginal orifice and anus) occurs in over three-quarters of vaginal births (Albers 1999; McCandlish 1998). Obstetric anal sphincter injury (OASI) occurs during childbirth and as the name suggests, involves the anal sphincter (the ring of muscle controlling the entrance to the rectum) and is classed as severe trauma. OASI has been reported in up to 18% (range 1.7% to 18%) of vaginal births (Harkin 2003; Hirayama 2012; Lowder 2007). There is wide variation in reported rates of OASI between countries which may be due to under or over reporting, differences in training in the recognition of OASI and the variety of tools used to identify injury. Tools used include: clinical examination, endoanal ultrasonography (use of an ultrasound probe to identify sphincter damage), anal manometry (use of a pressure sensitive probe to measure muscle tone) and patient questionnaires (to assess symptoms and quality of life). The occurrence of OASI also depends on several predisposing risk factors; therefore, the inclusion or exclusion or changes in the incidence of risk factors (for example, use of forceps and episiotomy) will alter the denominator population and influence the incidence rate (Abbott 2010).
The difficulties associated with estimating the rate of primary OASI are also associated with estimating the rate of recurrent OASI. Harkin 2003 reported a five-fold increase in the risk of recurrent OASI compared to the risk of injury for multiparous births, although these data included only 45 women having a spontaneous birth following primary OASI, of which only two sustained a second, third-degree tear. Conversely, Dandolu 2005 reported a lower combined rate of recurrent third- or fourth-degree tears compared to primary third- or fourth-degree tears, (5.76% versus 7.31%) but an increase in the rate of recurrent fourth-degree tears in women with previous primary fourth-degree tears compared to women with previous third-degree tears (7.73% versus 4.69%). The authors did not adjust for confounders, including parity and acknowledged that the reduction in the rates of modifiable risk factors such as forceps and episiotomy may have influenced the incidence rates. Peleg 1999 reported a doubling in the rate and Payne 1999 a three-fold increase in the rate of recurrent severe tears compared to those women with no tear or minor tear at the previous birth, with the highest recurrence rate in women who had undergone a repeat midline episiotomy. Although data regarding risk of recurrence of severe trauma are limited and conflicting, in the UK, the National Institute for Health and Clinical Excellence (NICE) intrapartum care guidance suggests the risk of recurrent severe trauma is similar to the risk of severe trauma at a first vaginal birth (NICE 2007).
Predisposing risk factors
Predisposing risk factors identified for primary OASI include: ethnicity (Wheeler 2012), episiotomy, forceps delivery, increasing maternal age, primiparity, induction and length of labour, vacuum extraction, neonatal head circumference and birthweight greater than 4 kg (Fizgerald 2007; Hirayama 2012; Kudish 2008; Williams 2005). Predisposing risk factors identified for recurrent OASI include: episiotomy, forceps and vacuum extraction (Dandolu 2005; Payne 1999; Peleg 1999). Use of episiotomy with forceps or vacuum seems to produce the greatest risk of recurrent anal sphincter injury (Dandolu 2005).
OASI is associated with an increased risk of short- and long-term morbidity which could seriously effect quality of life. Sequalae include: perineal pain (Macarthur 2004), dyspareunia (painful intercourse) (Rathfisch 2010), defaecatory dysfunction, and urinary and faecal incontinence (Fenner 2003; MacArthur 1997; Richter 2006). Perineal pain is an immediate consequence that may affect maternal and infant bonding, ability to breastfeed and to increase the risk of urinary retention and dyspareunia (Barrett 2000; Buhling 2006), and could influence well-being and the risk of depression (Brown 2000).
Possibly the most distressing adverse effect of OASI is anal incontinence related to anal sphincter injury and pudendal nerve damage (Fynes 1998). Four per cent of women report faecal incontinence following vaginal birth (MacArthur 1997). For women who have sustained OASI, the incidence of anal incontinence is related to the severity of the sphincter defect observed at follow up. For example, following clinically identified severe perineal trauma at the time of birth, 13% of women without identifiable sphincter defects on postnatal endo-anal ultrasound (EAUS) reported anal incontinence, whereas 64% with internal and external defects on EAUS reported anal incontinence (Laine 2011). Incontinence rates may worsen with time and following subsequent births irrespective of degree of perineal trauma sustained in these deliveries (Baghestan 2012; Bek 1992). Various factors have been identified that may help in determining the risk of anal incontinence following a subsequent birth; these include age, parity, presence and severity of symptoms, EAUS-identified injury and impaired sphincter function assessed by manometry.
Anal incontinence in the absence of identified OASI at the time of birth, may be in part due to pudendal nerve damage or unidentified anal sphincter damage. Sultan 1993 identified over 30% more anal sphincter injuries using EAUS compared with clinical examination alone. This difference may, however, be related to the experience of and/or technique used by the person undertaking the initial clinical examination rather than the superior sensitivity of EAUS (Andrews 2006).
Identification of Injury
All women who have sustained perineal trauma should have a systematic examination of the vagina, perineum and rectum, including rectal examination before and after perineal repair by an experienced practitioner trained in the recognition and management of perineal tears (NICE 2007; RCOG 2007). Methods of repair for OASI has been examined in a separate Cochrane review (Fernando 2006). To our knowledge, there are no reviews examining the type of repair suture for OASI or interventions for women in subsequent pregnancies following OASI for improving health.
Description of the condition
first degree – injury to skin only;
second degree – injury to the perineal muscles but not the anal sphincter;
third degree – injury to the perineum involving the anal sphincter complex:
3a – less than 50% of external anal sphincter thickness torn;
3b – more than 50% of external anal sphincter thickness torn;
3c – internal anal sphincter torn
fourth degree – injury to the perineum involving the anal sphincter complex (external and internal anal sphincter) and anal epithelium.
OASI includes third- and fourth-degree perineal tears. A third-degree perineal tear is defined as a partial or complete disruption of the anal sphincter muscles, which may involve either or both the external (EAS) and internal anal sphincter (IAS) muscles. A fourth-degree tear is defined as a disruption of the anal sphincter muscles with a breach of the anal or rectal mucosa (RCOG 2007).
Description of the intervention
Antenatal interventions for women who have sustained a previous obstetric anal sphincter injury may include the following: pelvic floor exercises that aim to strengthen the pelvic floor and have recently been found to reduce the risk of urinary incontinence (Stafne 2012); biofeedback training which uses computer-generated feedback from rectal balloons to a) improve patient awareness of the presence of faecal material in the rectum and b) to co-ordinate contraction of the external anal sphincter with relaxation of the internal sphincter and c) improve the force of the muscle (Miner 1990; Norton 2012); or stimulation of the sacral nerves that control the lower part of the bowel and sphincters by inserting electrodes in the lower back and connecting them to a pulse generator (Mowatt 2007). Other antenatal interventions include: perineal massage or creams that aim to reduce the risk of perineal tearing. Intrapartum interventions include: induction of labour to reduce the risk of macrosomia (infant birth weight greater than 4 kg) and subsequent risk of trauma; elective caesarean section to avoid vaginal and perineal trauma; vacuum as opposed to forceps to reduce the risk of trauma; selective episiotomy to reduce the risk of severe trauma; and different flexion techniques of the presenting fetal part to reduce the diameter and. in doing so, reduce the risk of subsequent trauma.
How the intervention might work
Interventions may aim to improve the integrity of the anal sphincter (pelvic floor muscle exercises, electrical stimulation), avoid trauma (elective caesarean section) or reduce the risk of trauma (medio-lateral episiotomy, vacuum and flexion techniques) to the perineum and anal sphincter and in doing so reduce the risk of adverse symptoms such as incontinence.
Why it is important to do this review
There are currently no systematic reviews or evidence-based guidance on interventions or strategies for women in subsequent pregnancies following obstetric anal sphincter injury to prevent or reduce the risk of further damage/trauma to the anal sphincter complex. Guidance based on robust evidence would allow us to improve the care in subsequent pregnancies for women who have previously sustained a third-degree tear, thus reducing morbidity and improving health.