VBAC Calculator – Vaginal Birth After Cesarean
Estimate VBAC success probability using evidence-based clinical factors for informed birth planning.
Enter maternal demographics, obstetric history, and current pregnancy details to estimate the likelihood of a successful vaginal birth after a previous cesarean section.
VBAC Calculator – Vaginal Birth After Cesarean
Estimate VBAC success probability using evidence-based clinical factors for informed birth planning.
About the VBAC calculator
Vaginal birth after cesarean section (VBAC) refers to a planned attempt to deliver vaginally when a woman has had one or more previous cesarean deliveries. VBAC is an important option in modern obstetric care because it can offer several advantages over repeat cesarean section, including shorter maternal recovery time, fewer surgical complications, lower risk of uterine adhesions, and in some cases better outcomes for future pregnancies. However, VBAC also carries a small but real risk of uterine rupture, which occurs in approximately 0.5–1% of attempted labors after cesarean.
Successful VBAC rates in published studies range broadly from 60% to 80%, with individual outcomes strongly influenced by patient-specific clinical factors. The most powerful predictor is whether the woman has previously delivered vaginally: women with at least one prior vaginal delivery — either before or after the cesarean — have substantially higher success rates than those with no prior vaginal births. The reason for the original cesarean also matters: non-recurring indications such as breech presentation or placenta previa generally predict better outcomes than recurring ones such as failure to progress or cephalopelvic disproportion.
Other factors that affect VBAC success include maternal age (younger women generally have higher success rates), pre-pregnancy BMI (obesity reduces VBAC success), gestational age at delivery, the presence of gestational diabetes or hypertension, and the method of labor induction if labor does not start spontaneously. Prostaglandin cervical ripening agents are associated with a higher risk of uterine rupture and are generally avoided in VBAC candidates; spontaneous onset of labor carries the lowest risk.
This calculator uses a scoring model derived from published VBAC predictor research to generate an estimated probability. It weighs each clinical factor based on its known association with VBAC success in large observational studies. The model is educational and simplified; it does not replace the validated nomograms developed by Grobman and colleagues using the MFMU Network dataset, which remain the gold standard for VBAC counseling in clinical practice.
Candidates for VBAC should be counseled in detail by their obstetric team. Absolute contraindications include prior classical (vertical) uterine incision, prior uterine rupture, and certain uterine surgeries. Attempted VBAC should occur in a facility capable of emergency cesarean delivery. Continuous fetal heart rate monitoring during labor is standard of care.
This tool is for informational and educational use only. It should not be used as a substitute for individualized clinical assessment by a qualified healthcare provider.
VBAC probability examples
Click any example button to load a preset scenario into the calculator.
| Patient profile | Estimated probability | Interpretation |
|---|---|---|
| Age 26, 1 prior vaginal, 1 prior cesarean (breech), GA 39 wk, BMI 24, no complications, spontaneous labor | ~95% | Favorable candidate. Young age, prior vaginal delivery, non-recurring indication, and low BMI all maximize success probability. |
| Age 32, no prior vaginal, 1 prior cesarean (fetal distress), GA 38 wk, BMI 28, no complications, Pitocin induction | ~55% | Cautious candidate. No prior vaginal delivery and Pitocin induction reduce the probability significantly compared to spontaneous labor. |
| Age 35, no prior vaginal, 2 prior cesareans (failure to progress), GA 37 wk, BMI 32, GDM, hypertension, prostaglandin | ~10% | Challenging candidate. Multiple adverse factors including recurring indication, prostaglandin use, and medical comorbidities significantly lower success probability. |
| Age 24, 2 prior vaginal, 1 prior cesarean (placenta previa), GA 40 wk, BMI 22, no complications, spontaneous labor | ~95% | Optimal candidate. Multiple prior vaginal deliveries and a non-recurring indication provide the highest success probability. |
How to use the VBAC calculator
- Enter maternal age and current gestational age in weeks.
- Input the number of previous vaginal deliveries and previous cesarean sections.
- Select the indication for the most recent cesarean section from the dropdown.
- Enter pre-pregnancy BMI and select gestational diabetes, hypertension, and planned induction method.
- Click Calculate VBAC Probability to see the estimated success rate and candidate category. Discuss results with your obstetrician.
VBAC calculator FAQ
What is the overall success rate of VBAC?
Population studies show that roughly 60–80% of women who attempt VBAC deliver vaginally. Success rates are higher in women with prior vaginal delivery, non-recurring cesarean indications, and spontaneous onset of labor, and lower in women with multiple prior cesareans, obesity, or requiring induction.
What is uterine rupture and how common is it?
Uterine rupture is a tear through the uterine wall at or near the previous cesarean scar. It occurs in approximately 0.5–1% of VBAC attempts and can be life-threatening for both mother and baby. Signs include sudden severe abdominal pain, abnormal fetal heart rate, and maternal hemodynamic instability. Immediate emergency cesarean is required.
Does having a prior vaginal birth significantly help VBAC chances?
Yes. A history of at least one successful vaginal delivery — whether before or after the cesarean — is the single strongest predictor of VBAC success. Studies show VBAC success rates of 85–90% in women with a prior vaginal delivery, compared to about 60–65% in women without any prior vaginal birth.
Is Pitocin safe for VBAC labor induction?
Oxytocin (Pitocin) augmentation or induction can be used for VBAC but carries a modestly higher risk of uterine rupture compared to spontaneous labor. Prostaglandin cervical ripening agents are generally contraindicated in VBAC because they are associated with a substantially higher rupture risk. Cervical ripening with a balloon catheter is an alternative sometimes used.
What makes someone a poor candidate for VBAC?
Absolute contraindications include a prior classical (high vertical) uterine incision, prior uterine rupture, certain prior uterine surgeries, and situations where vaginal delivery is otherwise contraindicated. Relative risk factors that reduce VBAC suitability include multiple prior cesareans, obesity (BMI > 30–35), age over 40, short interpregnancy interval, and gestational age beyond 40 weeks.
Should VBAC be attempted at any hospital?
ACOG and major obstetric societies recommend that VBAC be attempted only in facilities equipped for immediate emergency cesarean delivery, with in-house obstetric, anesthesia, and neonatal teams available. Continuous electronic fetal monitoring during VBAC labor is standard. Transfer of care to an appropriate facility before labor is important if these resources are not available.