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Overview and Implications

Lacerations are common after vaginal birth. Trauma can occur on the cervix, vagina, and vulva, including the labial, periclitoral, and periurethral regions, and the perineum (American College of Obstetricians and Gynecologists (ACOG), 2018). A woman's safety during childbirth can be assessed by looking at potentially avoidable tearing of the perineum (Organization for Economic Co-operation and Development (OECD), 2019) and other obstetrical injuries to the pelvic organs during vaginal deliveries. While it is not possible to prevent these types of tears in all cases, they can be reduced by appropriate labour management and high-quality obstetric care (OECD, 2019).

Obstetric anal sphincter injuries (OASIS)

(also known as Obstetric Anal Sphincter Injury - OASI)

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) refers to 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 (Aasheim et al., 2017; Harvey & Pierce, 2015). The table below lists the classification of OASIS from first to fourth degree.

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

(Royal College of Obstetricians and Gynaecologists (RCOG), 2015; Harvey & Pierce, 2015)

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 (Harvey & Pierce, 2015).

Canada lags behind other Organisation for Economic Co-operation and Development (OECD) countries on measures of patient safety.  Specifically, obstetrical trauma rates in Canada are twice as high as the OECD average (without instrument = 1.4, instrument = 5.5), and are not improving (Canadian Institute for Health Information (CIHI), 2019a).

The incidence of obstetric and sphincter injuries varies widely across our country. In 2017-18, Canada's average rate of obstetric and sphincter injuries in vaginal deliveries without instrument assistance was 3.1 per 100 deliveries with provincial rates ranging between 1.3 and 4.2 (CIHI, 2019b).

Assisted vaginal deliveries increase the risk of significant perineal trauma (OECD, 2019; Hobson et al., 2019; Harvey & Pierce, 2015) and obstetrical anal sphincter injuries are more commonly associated with forceps deliveries than with vacuum-assisted vaginal deliveries (Hobson et al., 2019, Harvey & Pierce, 2015).  In vaginal deliveries with instrument assistance, the average Canadian rate was 16.4 per 100 deliveries, with provincial rates ranging between 6.0 and 24.1 (CIHI, n.d.).

Other risk factors for perineal trauma include: Asian ethnicity, primiparity, birth weight greater than four kg, shoulder dystocia, occipito-posterior position, and prolonged second stage labour (RCOG, 2015; Harvey & Pierce, 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 Caesarean delivery (CD), particularly when the Caesarean is performed during the second stage of labor (either due to second-stage arrest or for fetal indications) (Wong et al., 2016).

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). 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).

Uterine rupture

Uterine rupture during labour, a rare but severe obstetric complication (Andersen et al., 2016), is defined as spontaneous tearing of the uterus that may result in the fetus being expelled into the peritoneal cavity. Uterine rupture can occur during late pregnancy or active labor. It occurs most often along healed scar lines in women who have had prior Caesarean deliveries. Other predisposing factors include congenital uterine abnormalities, trauma, and other uterine surgical procedures such as myomectomies or open maternal-fetal surgery (Moldenhauer, 2020). Uterine rupture is an urgent situation that requires immediate attention and laparotomy in order to attempt to decrease maternal and perinatal morbidity and mortality (Health Quality Ontario (HQO), 2018; Dy et al., 2019).

People who labour after a previous Caesarean have a higher risk of uterine rupture than those who choose an elective repeat Caesarean section (HQO, 2018).  Despite this risk it is important to note that a vaginal birth after Caesarean (VBAC) is associated with decreased maternal morbidity and a decreased risk of complications in future pregnancies as well as a decrease in the overall Caesarean delivery rate at the population level (ACOG, 2019).

In Canada, the primary Caesarean section rate has remained stable at 17.8 per cent, however the proportion of women with previous CS who underwent a repeat CS, has steadily increased. This steady rise in repeat CS is accompanied by a decline in women having a Trial of Labour after a previous Caesarean section (TOLAC) and vaginal birth after Caesarean (VBAC) (Dy et al., 2019).

The SOGC offers evidenced-based guidelines for the provision of a trial of labour after Caesarean section (Dy et al., 2019). Key messages from their Clinical Practice Guideline, Trial of Labour after Caesarean are:

  1. TOLAC is recommended in women without contraindications to labour and vaginal birth, with a previous vaginal birth, and/or those who present in spontaneous labour.
  2. The relative risk of maternal death is higher for elective repeat Caesarean section (ERCS) and the relative risk of uterine rupture is higher for TOLAC, but the absolute risks of either of these outcomes is low.
  3. The baseline risk of uterine rupture with a TOLAC is 0.47 per cent.
  4. Women planning a TOLAC should be advised that the relative risk of perinatal mortality is higher with TOLAC compared to ERCS, but the absolute risk is low.
  5. Continuous fetal monitoring and access to immediate laparotomy are essential when planning a TOLAC.

A woman and her health care provider must decide together whether an appropriate situation exists for considering TOLAC (Dy et al., 2019). Informed, documented, and shared decision making of the risks of TOLAC versus ERCS is essential. All centres should have a plan for managing uterine rupture. Drills or other simulations may be useful in preparing for these rare emergencies.


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

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