Uterine rupture, the complete separation of all three layers of the uterus (endometrium, myometrium, parametrium) is a life-threatening surgical emergency for both mother and fetus. Most cases of uterine rupture occur in a scarred uterus (i.e previous cesarean section or gynecologic surgical procedures involving entering the myometrium), but can occur in labour dystocia when operative vaginal or cesarean section cannot be obtained.
The biggest risk factor for uterine rupture is a trial of labour (TOL) after cesarean section- this increases the risk of rupture by 0.47% (vs. 0.026% with electrive repeat cesarean section) . This risk is highest in those with TOL over 40 weeks gestation. This is due to the uterine scar, therefore other reasons for uterine scar including myomectomy, uterine perforation, or salpingectomy with cornual resection may also increase the risk for uterine rupture.
Other risk factors include:
- Short interval between cesarean section and vaginal delivery (less than 18 months)
- 2 or more previous cesarean sections
- Excessive use of uterotonic drugs*
- Uterine abnormalities
- Placental abnormalities- ex. accreta
- Fetal macrosomia
- Multiple gestation
- Trauma, including: External cephalic version, forceps delivery, manual delivery of placenta, motor vehicle accidents, assault etc
*Of note, oxytocin is not contraindicated in TOL after cesarean section but should involve appropriate counselling and be used carefully (increases risk of uterine rupture to 1.1%, ~ double the baseline risk). Mechanical induction of labour such as foley catheter insertion is not contraindicated in TOL after cesarean section. Other medical induction of labour methods like prostaglandin E2 and E1 are not recommended in TOL after cesarean due to increased risk of uterine rupture at term (increases risk of uterine rupture to 2%). The highest risk induction of labour method was misoprostol, associated with 6% risk of uterine rupture. The overall risk of uterine rupture with any method of induction of labour ranges between 0.7-2.7%. This risk of rupture with induction is the highest for those >40 weeks gestation.
Women undergoing TOL after cesarean section or at risk of uterine rupture should be in a centre where immediate cesearean section is available and should be on continuous fetal monitoring, as fetal heart rate abnormalities may be a key sign of uterine rupture (ie they are likely not suitable for home births). If this is not available at the obstetrical care centre, exceptions can be made with appropriate counselling and consent of the patient. This should involve discussion of possible delay of surgery and associated risks.
Outcomes associated with uterine rupture
Counselling for TOL after cesarean section and risk of uterine rupture should include the possibility of:
- Maternal mortality (1.6 to 3.8 per 100 000)
- Severe hemorrhage requiring blood transfusion (6.6 per 1000)
- Hysterectomy (1.7 per 1000)
- Infection (46 per 1000)
The absolute risk of these maternal outcomes is low. If after discussion, the patient does not consent to a TOL after cesarean section due to the increased risk of uterine rupture and there is no capacity for immediate ceserean section, the patient should be transfered to a site where this service is available. Regardless, if required, the standard of care for cesarean section for suspected uterine rupture is within 30 minutes.
Neonatal morbidity and mortality are mostly associated with uterine rupture and risks should be discussed with the patient. These include:
- Risk of hypoxic ischemic encephalopathy
- Neonatal death (6.2% with uterine rupture)
The absolute risk of these neonatal outcomes is low.