What is the risk of uterine rupture in an unscarred uterus during labor or prior to labor?

From the Guidelines

The risk of uterine rupture in an unscarred uterus is approximately 1 in 8,000 to 1 in 15,000 pregnancies (0.006-0.013%). This condition is extremely rare and can occur either during labor or before labor begins. According to the American College of Obstetricians and Gynecologists (ACOG) guidelines, as reported in the American Family Physician journal 1, the use of certain medications such as misoprostol for cervical ripening and induction of labor may increase the risk of uterine rupture, especially in women with previous cesarean deliveries. However, the risk in unscarred uteri is still relatively low.

Key Points

• The risk of uterine rupture in an unscarred uterus is significantly lower than in scarred uteri, particularly those with previous cesarean deliveries.
• Risk factors that may increase the risk of uterine rupture in an unscarred uterus include grand multiparity, advanced maternal age, placental abnormalities, trauma, uterine anomalies, excessive use of oxytocin, and obstructed labor.
• The condition presents with sudden severe abdominal pain, vaginal bleeding, fetal distress, and maternal shock, and requires immediate surgical intervention.
• The maternal mortality rate is approximately 0-1%, but fetal mortality is much higher at 40-75% when rupture occurs.

Clinical Considerations

• Healthcare providers should remain vigilant for this potentially catastrophic complication, especially in the presence of risk factors.
• The use of medications such as misoprostol should be carefully considered and monitored, especially in women with risk factors for uterine rupture.
• Continuous monitoring of fetal heart rate and uterine activity is essential during labor induction or augmentation, especially when using medications such as oxytocin or prostaglandins 1.

From the Research

Incidence of Uterine Rupture in Unscarred Uterus

• The incidence of uterine rupture in an unscarred uterus is rare, with studies suggesting it occurs in less than 1% of pregnancies 2, 3.
• A review of the literature found 84 case reports of spontaneous rupture of the unscarred uterus, with a mean maternal age of 29.3 years and 45.2% of women being nulliparous 3.
• The most common clinical presentations of uterine rupture in an unscarred uterus include abdominal pain, signs of hypovolemic shock, fetal distress, and vaginal bleeding 3.

Risk Factors for Uterine Rupture in Unscarred Uterus

• The use of uterotonic drugs for induction or augmentation of labor is a common risk factor for uterine rupture in an unscarred uterus 3.
• A prior curettage procedure is also a risk factor for uterine rupture in an unscarred uterus 3.
• Other risk factors include mismanaged labor, grand multiparity, and obstructed prolonged labor 4.
• Fetal macrosomia and nonreassuring fetal status are also associated with an increased risk of uterine rupture or dehiscence 5.

Maternal and Fetal Outcomes

• Uterine rupture in an unscarred uterus is associated with severe maternal and neonatal outcomes, including maternal death, perinatal death, and hysterectomy 4, 3.
• Perinatal mortality is higher in developing countries than in developed countries 3.
• The most common management of uterine rupture is hysterectomy, which was performed in 36.9% of cases in one study 3.

Prevention and Management

• Proper management of labor, including careful monitoring and judicious use of oxytocin, can help reduce the risk of uterine rupture in an unscarred uterus 5, 6.
• A delivery plan should include assessment of cesarean history and fetal macrosomia, and intrapartum monitoring for nonreassuring fetal status 5.
• Simplified and standardized intrapartum management, precise protocol, and cautious monitoring of oxytocin use in trial of labor after cesarean (TOLAC) are necessary to reduce the risk of uterine rupture 6.