The primary danger of a VBAC (vaginal birth after cesarean) is uterine rupture, where the scar from a previous C-section tears open during labor. This happens in roughly 0.3% to 0.7% of attempts with one prior cesarean, meaning it affects fewer than 1 in 100 women. That rate is low, but the consequences when it does occur can be severe for both mother and baby, which is why the risk gets so much attention.
What makes this topic complicated is that a planned repeat C-section carries its own set of dangers, including a maternal mortality rate roughly three and a half times higher than a successful VBAC (13.4 versus 3.8 per 100,000 live births). So the real question isn’t whether VBAC is dangerous in absolute terms, but how its specific risks compare to the alternative and which factors tip the balance for individual women.
Why Uterine Rupture Is the Central Concern
Every cesarean delivery leaves a scar on the uterus. When labor contractions push against that scar during a VBAC attempt, there’s a small chance the tissue gives way. The type of scar matters enormously. A low transverse incision, the most common type used today, carries a rupture risk of 0.2% to 1.5%. A classical incision, which runs vertically through the upper portion of the uterus, raises that risk to 4% to 9%. T-shaped extensions fall into that same higher range. If you don’t know what type of incision was made on your uterus (which is different from your skin incision), your medical records from the prior surgery will specify it.
When rupture does happen, it can cause life-threatening hemorrhage in the mother and cut off the baby’s oxygen supply. In the large MFMU Cesarean Registry cohort, 40% of newborns delivered after a uterine rupture were admitted to the NICU, and 6.2% developed hypoxic-ischemic encephalopathy, a type of brain injury caused by oxygen deprivation. Perinatal mortality related to uterine rupture during a VBAC attempt ranges widely in the literature, from 0.01% to as high as 26%, with the worst outcomes occurring when the placenta separates or the baby is pushed outside the uterus entirely. These catastrophic scenarios are rare, but they explain why hospitals offering VBAC typically require the ability to perform an emergency C-section within minutes.
What Happens When a VBAC Attempt Fails
Not every VBAC attempt ends in vaginal delivery. Success rates sit around 84% in well-selected candidates with one prior cesarean, but that means roughly 1 in 6 women will need an unplanned C-section during labor. This “failed TOLAC” (trial of labor after cesarean) scenario tends to carry more complications than either a successful VBAC or a planned repeat C-section. The combination of hours of labor followed by emergency surgery increases the chance of infection, heavier blood loss, and a longer recovery. In a Chinese population-based study, seven patients experienced uterine rupture during their labor attempt, though none required a hysterectomy.
The distinction matters because anything that lowers your probability of a successful vaginal delivery also raises your overall risk profile, since it makes that emergency surgical scenario more likely.
Factors That Increase the Risk
Several variables shift the odds meaningfully:
- Number of prior cesareans. One previous C-section carries a rupture rate of about 0.72%. Two prior cesareans roughly double it to 1.36%, with the success rate dropping from 76.5% to 71.1%.
- Short interval between deliveries. Delivering again less than 18 months after a cesarean is associated with a higher risk of rupture. The scar tissue needs time to heal fully, and pregnancies spaced too closely together don’t allow that.
- Higher BMI. Women with a BMI of 30 or above have a 57% VBAC success rate compared to 69% for those under 30. As BMI climbs further, success drops further: 62.6% for class I obesity, 54.2% for class II, and just 38.6% for class III. Lower success rates translate directly into higher rates of emergency intervention.
- Type of uterine incision. A classical or T-shaped incision raises rupture risk to 4% to 9%, which is why most guidelines consider these a contraindication for attempting VBAC at all.
How Labor Induction Changes the Equation
Spontaneous labor, where contractions begin on their own, is the safest scenario for a VBAC attempt. When labor needs to be induced, the method used has a significant impact on rupture risk. Oxytocin (the synthetic version of the hormone your body naturally produces during labor) may slightly increase the risk and needs to be used carefully. In one study, the rupture rate with oxytocin induction was 2%.
Prostaglandin medications are where things get more dangerous. One type of prostaglandin gel used for cervical ripening significantly increased rupture risk in studies. The drug misoprostol is particularly concerning. In one comparison, misoprostol was associated with an 18.8% rupture rate versus zero ruptures in the comparison group. Canadian obstetric guidelines explicitly state that misoprostol should not be used during a VBAC attempt. Combining prostaglandins with oxytocin pushed the rupture rate to 4.5% in one study. If your provider recommends inducing labor during a VBAC attempt, the specific method they plan to use is worth asking about.
Mechanical methods like a foley catheter balloon, which physically opens the cervix without medication, did not show an increased rupture risk compared to spontaneous labor.
Putting the Risk in Context
VBAC’s dangers are real but concentrated. For a woman with one prior low transverse cesarean, a pregnancy spaced at least 18 months apart, and spontaneous labor onset, the rupture risk is under 1% and the success rate is high. Stack multiple risk factors together, such as two prior cesareans, a short interpregnancy interval, and induced labor, and the math shifts considerably.
It’s also worth weighing the risks of the alternative. Each additional cesarean delivery increases the chance of serious surgical complications in future pregnancies, including abnormal placenta attachment, bladder injury, and heavier bleeding. The maternal mortality data showing a rate of 13.4 per 100,000 for planned repeat cesareans versus 3.8 per 100,000 for VBAC reflects these cumulative surgical risks. For women planning multiple future pregnancies, a successful VBAC can actually reduce long-term danger.
The core tension is that VBAC concentrates its risk into a narrow, acute window (labor and delivery), while repeat cesareans spread their risk across current and future surgeries. Neither option is risk-free, and the safest choice depends heavily on your individual history, your body, and the resources available at your delivery hospital.