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Overview and Implications

Obstetric Trauma

Perineal trauma occurs either spontaneously with vaginal delivery or secondarily as an extension to an episiotomy. Severe perineal trauma can involve damage to the anal sphincters and anal mucosa. Obstetric anal sphincter injuries (OASIS) include third and fourth degree perineal tears. Third degree tears involve a partial or complete disruption of the anal sphincter complex which includes the external anal sphincter and the internal anal sphincter. Fourth degree tears involve disruption of the anal mucosa in addition to division of the anal sphincter complex (Aascheim et al, 2011; SOGC, 2015). Please see the table below for the classification of OASIS from first to fourth degree:

Classification of OASIS (RCOG, 2015 & SOGC, 2015)

First degreeInjury to perineal skin only
Second degree            Injury to perineum involving perineal muscles but not involving the anal sphincter
Third degree Injury to perineum involving the anal sphincter complex:
3a Less than 50% of external anal sphincter (EAS) thickness torn
3b More than 50% of EAS thickness torn
3c Both EAS and internal anal sphincter (IAS) torn
Fourth degree Injury to perineum involving the anal sphincter complex (EAS and IAS) and anal epithelium

Obstetric anal sphincter injuries can have a significant impact on women by impairing their quality of life in both the short and long term. One of the most distressing immediate complications of perineal injury is perineal pain. Short-term perineal pain is associated with edema and bruising, which can be the result of tight sutures, infection, or wound breakdown. Perineal pain can lead to urinary retention and defecation problems in the immediate postpartum period. In the long term, women with perineal pain may have dyspareunia and altered sexual function. Additionally, complications of severe perineal tears include abscess formation, wound breakdown, anal incontinence and rectovaginal fistulae (SOGC, 2015).

Although the true prevalence of anal incontinence related to obstetric anal sphincter injuries may be underestimated, it has been determined that it ranges between 15 and 61 per cent, with a mean of 39 per cent (SOGC, 2015; Sultan & Kettle, 2009).

The incidence of obstetric and sphincter injuries varies widely between countries and within hospitals in the same country. In 2011, Canada's crude rate of obstetric and sphincter injuries in vaginal deliveries with instrument assistance was 17 per 100 deliveries, and in vaginal deliveries without instrument assistance, it was 3.1 per 100 (OECD, 2013). This is higher than rates in the United Kingdom, Europe and Asia, however, there is likely to be significant variation in incidence reporting in addition to differences in obstetric practices (Dickinson, 2013; Hirayam et al, 2012).

Instrumental deliveries increase the risk of significant perineal trauma. Obstetrical anal sphincter injuries are more commonly associated with forceps deliveries than with vacuum-assisted vaginal deliveries, however the use of the vacuum extractor may also produce anal sphincter injury either directly or through the concomitant use of an episiotomy (Dickinson, 2013; Lacker, 2012; OECD, 2013; SOGC, 2015).  Other risk factors include; Asian ethnicity, primiparity, birth weight greater than four kg, shoulder dystocia, occipito-posterior position, and prolonged second stage labour (RCOG, 2015; SOGC, 2015).

Cervical laceration
Intrapartum cervical lacerations are traditionally thought of as occurring due to the delivery of the fetus through the cervix at the time of vaginal birth. However, cervical lacerations may also be noted at the time of cesarean delivery (CD), particularly when the cesarean is performed during the second stage of labor (either due to second-stage arrest or for fetal indications) (Wong, et al. 2016), from an extension of the hysterotomy incision.

Although many studies have been published on vaginal and perineal lacerations, data on the incidence, clinical characteristics, and risk factors of intrapartum cervical lacerations is sparse (Melamed, et al. 2009). Based on the limited literature, it has been reported that intrapartum cervical lacerations are common, with an overall incidence that ranges from 25 to 90 per cent in different reports. However, most cases are asymptomatic and are noted only on routine examination of the cervix (Melamed, et al. 2009). Parikh et al, (2007) reported that while cervical lacerations occur in more than half of vaginal deliveries, they are less and 0.5 cm in length and rarely require repair.

Clinically significant cervical lacerations have been reported to complicate 0.2 to 4.8 per cent of all vaginal deliveries. Clinically significant cervical lacerations have been defined as lacerations that were associated with abnormal vaginal bleeding, those requiring cervical suturing or those lacerations that extend to involve the lower uterine segment or the vaginal wall (Melamed, et al. 2009). 

There is consensus across three studies that cervical cerclage is a risk factors for cervical lacerations (Landy et al. 2011; Melamed, et al. 2009; Parikh et al, 2007). Other risk factors identified but lacking consensus across the three studies are precipitous labor, episiotomy (Melamed, et al. 2009) vacuum extraction (Landy et al 2011; Melamed, et al. 2009) and labor induction (Landy et al. 2011; Parikh et al, 2007).

Uterine rupture
Uterine rupture during labour, a rare but severe obstetric complication (Andersen et al, 2016), is defined as complete separation of the myometrium with or without extrusion of the fetal parts into the maternal peritoneal cavity and requires emergency Caesarean section or postpartum laparotomy (SOGC, 2018). The most common circumstance in which uterine rupture occurs is in women attempting vaginal birth after caesarean (VBAC) (Lang 2010). Evidence continues to suggest that women who plan a Trial of Labour (TOL) after caesarean birth, experience a greater risk of uterine rupture than women planning elective repeat Caesarean section (ERCS) (VBAC CPG Working Group, 2011).

Despite the risk of uterine rupture that comes with a TOL after caesarean, it is important to note that a VBAC is associated with decreased maternal morbidity and a decreased risk of complications in future pregnancies (American College of Obstetricians and Gynecologists, 2017).  A TOL after caesarean should be considered in women who present for prenatal care with a history of previous caesarean birth.  In certain situations, a TOL after caesarean will be contraindicated and a repeat Caesarean section will be advised, but in most cases, successful vaginal birth can be safely achieved for both mother and infant. Women and their healthcare providers will need to discuss the risks and benefits of VBAC when planning the birth (SOGC, 2018).

Risk of Uterine Rupture
The type and location of the previous uterine incision helps to determine the risk of uterine rupture. The incidence of uterine rupture is 0.2 to 1.5 per cent in women who attempt labour after a transverse lower uterine segment incision and 1 to 1.6 per cent in women who have had a vertical incision in the lower uterine segment. The risk is 4 to 9 per cent with a classical or "T" incision (SOGC, 2018).

Additional risk factors for uterine rupture with TOL after Caesarean:

  • Those with a prior uterine rupture (American College of Obstetricians and Gynecologists, 2017).
  • Those with extensive transfundal uterine surgery (American College of Obstetricians and Gynecologists, 2017).
  • Those who had more than one Caesarean section (SOGC, 2018)
  • The use of medication to induce labour (SOGC, 2018, American College of Obstetricians and Gynecologists, 2017; Ophir 2012).
  • Prolonged labour with augmentation (SOGC, 2018) 
  • Delivery interval less than 18 months (SOGC, 2018)

Although, it has been reported that these factors may increase the chance of uterine rupture with TOL after Caesarean section, limited data and varying results suggests these factors require more study (SOGC, 2018; American College of Obstetricians and Gynecologists, 2017).

Protective Factors of Uterine Rupture with VBAC:

  • Prior vaginal delivery.  It has been found that the risk of uterine rupture decreases after the first successful VBAC. (SOGC, 2018; American College of Obstetricians and Gynecologists 2017; VBAC CPG Working Group, 2011).
  • Delivery intervals greater than 24 months (VBAC CPG Working Group, 2011).
Contraindications to TOL after Caesarean: (SOGC, 2018; VBAC CPG Working Group, 2011)

Previous classical or inverted T uterine scar.

  • Previous hysterotomy or myomectomy entering the uterine cavity.
  • Previous uterine rupture.
  • Presence of a contraindication to labour such as placenta previa or transverse lie.
  • A woman declining TOL after Caesarean and requesting an ERCS. 

It has been reported that 50 to 88 per cent of women who have had a previous caesarean delivery can successfully deliver vaginally (SOGC, 2018; VBAC CPG Working Group, 2011, Kuehn 2012; Scott, 2013). Among women receiving care from Ontario midwives in 2006 to 2008, 71 per cent of women with a history of CS who opted for VBAC ultimately delivered vaginally (VBAC CPG Working Group, 2011). Despite the relative success in vaginal delivers after previous CS, the threat of uterine rupture has often dissuaded women and their physicians from attempting a trial of labor (Kuehn, 2012; Scott, 2013).

Though rare, uterine rupture is a significant risk associated with having had a previous CS (VBAC CPG Working Group, 2011) and when they do occur, physicians must intervene quickly to prevent death or severe injury to the child and the mother (Kuehn 2012; Scott, 2013).


Reduce the incidence of obstetric trauma captured in this clinical group.

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