Attempting a vaginal birth after a previous cesarean, often called VBAC, carries a small but real risk of serious complications, the most significant being uterine rupture at the site of the previous surgical scar. That risk sits at about 1 in 200 (0.5%) for women with one prior low-transverse cesarean. Most women who attempt it succeed: 60% to 80% deliver vaginally, depending on individual factors. But understanding the specific risks, and what raises or lowers them, is essential to making an informed choice.
Uterine Rupture: The Primary Concern
Uterine rupture is the complication that sets VBAC apart from any other vaginal delivery. It happens when the scar from a previous cesarean tears open during labor, sometimes partially and sometimes completely through the uterine wall. With one prior low-transverse incision (the most common type, a horizontal cut across the lower uterus), the rupture rate is less than 1%. With two previous cesareans, that rate climbs slightly to 1% to 2%.
When rupture does occur, it can cause severe hemorrhaging in the mother and cut off oxygen to the baby. Among the small number of babies born during a rupture event, about 5.6% experience severe, permanent neurological injury. The overall risk of permanent neurological harm to a baby during any VBAC attempt is very low, at roughly 0.46 per 1,000 women, but it is not zero. If rupture is detected, an emergency cesarean is performed within minutes, which is why where you deliver matters enormously.
How the Type of Previous Incision Changes Risk
Not all cesarean scars carry the same risk. A low-transverse incision, the horizontal cut used in most modern cesareans, has the lowest rupture rate and is considered appropriate for a VBAC attempt. A classical incision, which is vertical and extends higher on the uterus, carries a much higher rupture risk. VBAC is considered contraindicated with a classical scar.
For less common incision types like T-shaped, J-shaped, or low vertical cuts, the evidence on safety is limited. These cases require individual assessment by an experienced obstetrician. If you’re unsure what type of incision you had, your operative report from the previous cesarean will specify it, and it’s worth asking for that information early in your pregnancy.
Risk to the Baby
The absolute risk of a baby dying during a VBAC attempt is low but roughly double that of a planned repeat cesarean: 0.13% versus 0.05%. Most of that increased risk is tied directly to the possibility of uterine rupture. Outside of rupture, rates of stillbirth during labor were statistically similar between the two groups in large studies.
The practical takeaway is that for every 1,000 women attempting VBAC, about one additional baby may die compared to planned repeat cesarean. That’s a small number, but it’s the kind of information that weighs differently for every family.
Maternal Risks Compared to Repeat Cesarean
A successful VBAC generally carries fewer complications for the mother than a repeat cesarean, since it avoids major abdominal surgery. But a VBAC attempt is not always successful, and a failed attempt that ends in an unplanned cesarean during labor tends to carry higher complication rates than either a successful VBAC or a planned repeat cesarean.
When researchers compared the two paths overall, blood transfusion rates were similar: about 0.9% for women attempting VBAC and 1.2% for those choosing a repeat cesarean. Infection risk was also broadly comparable, though women attempting VBAC had somewhat higher rates of uterine lining infection and infection of the amniotic membranes. Wound infection rates were not significantly different. Febrile episodes (postpartum fevers) were actually lower in the VBAC group.
The key nuance: these numbers combine successful and failed VBAC attempts. A straightforward vaginal delivery has a shorter recovery, lower infection risk, and avoids surgical complications entirely. But if you end up laboring for hours and then needing an emergency cesarean, you face the risks of both labor and surgery.
Timing Between Pregnancies
How long your uterine scar has had to heal matters. A short gap between pregnancies significantly increases the chance of rupture. Women with an interpregnancy interval of less than six months had roughly 2.7 times the risk of uterine rupture compared to those who waited longer. They also faced about three times the risk of needing a blood transfusion and nearly double the risk of other major complications.
An interval of 6 to 11 months still showed elevated risk, though less dramatically. Most guidelines suggest waiting at least 18 months between delivery and the next conception (which translates to roughly 27 months between births) to give the scar adequate time to strengthen. Longer intervals did not increase major complications.
What Predicts a Successful VBAC
Your odds of success vary substantially based on why you had the first cesarean and your current circumstances. The single strongest predictor is having had a previous vaginal delivery. Women who have already had one successful VBAC have a 93% chance of succeeding again. Those who had a vaginal delivery before their cesarean succeed about 85% of the time.
The reason for your previous cesarean also matters. If the first cesarean was for a non-recurring issue like breech position or fetal distress, VBAC success rates are high, around 89% for breech. If it was for failure to progress or a mismatch between the baby’s head and the pelvis, success rates drop to 50% to 67%, though two-thirds of women in this group still deliver vaginally.
Several other factors shift the odds:
- Maternal BMI: Women with a normal BMI succeed about 70.5% of the time, compared to 54.6% for women classified as obese.
- Maternal age: Younger women have higher success rates. Being 40 or older independently lowers the chance of success and increases the risk of stillbirth.
- Baby’s size: When the baby weighs over 4 kg (about 8.8 pounds) and the mother has no prior vaginal delivery, success rates fall below 50%.
- Diabetes: Both gestational and pre-existing diabetes reduce the likelihood of successful vaginal delivery.
- Cervical dilation at admission: Women who arrive at the hospital already in active labor (cervix dilated past 3 cm) have a much stronger chance of delivering vaginally than those admitted in early labor.
- Number of prior cesareans: Having two previous cesareans lowers success somewhat (62% to 75%) but doesn’t rule out VBAC.
Where You Deliver Matters
Because uterine rupture requires an emergency cesarean within minutes to protect both mother and baby, VBAC attempts are safest at facilities that can mobilize a surgical team immediately. This typically means a hospital with in-house obstetric and anesthesia coverage, not a birthing center or home setting. If your local hospital cannot guarantee rapid surgical access, a planned repeat cesarean may be the safer choice regardless of how favorable your other risk factors are.
Continuous fetal monitoring during labor is standard for VBAC attempts, since changes in the baby’s heart rate pattern are often the earliest warning sign of rupture. This does limit your mobility during labor compared to an unmonitored birth, but it provides a critical safety layer that can mean the difference between a good outcome and a devastating one when complications arise quickly.