5 Factors That Predict a Successful VBAC

Not every woman attempting a VBAC has the same odds of success. The population-level range — 60% to 80%, according to ACOG — is wide because individual factors shift the number meaningfully in either direction. Here's what actually matters, based on the same clinical research behind the MFMU (Maternal-Fetal Medicine Units) Network VBAC prediction model, sometimes also called the NICHD VBAC calculator.

1. A Prior Vaginal Delivery

This is the single strongest predictor of VBAC success. If you've delivered vaginally before — whether that was before or after your c-section — your odds of a successful VBAC go up substantially. Your body has demonstrated it can do this before.

2. The Reason for Your Prior C-Section

Not all c-sections happen for the same reason, and the reason matters. If your prior cesarean was for a one-time issue — a breech baby, fetal distress, or placenta previa — your odds of a successful VBAC are generally high, since that circumstance likely won't repeat.

If your prior c-section was for "failure to progress" (arrest of dilation or descent), your odds are somewhat lower, but a VBAC is still very much possible. Every labor is different.

3. Maternal Age and BMI

Younger age and a lower BMI at delivery both correlate with higher VBAC success rates in the research. Neither is something you can change on short notice, but they're part of why your personal probability differs from the population average — and part of why individualized counseling matters more than a general statistic.

4. Spontaneous vs. Induced Labor

Labor that starts on its own is associated with a higher chance of VBAC success than labor that needs to be induced. This doesn't mean induction rules out VBAC — many inductions succeed — but it's one more variable your provider will factor into your specific plan.

5. A Prior Successful VBAC

If you've already had a successful VBAC in a previous pregnancy, that's a strong positive signal for this one too. Each successful VBAC tends to reinforce the likelihood of the next.

What You Can't Control (And Shouldn't Blame Yourself For)

Some predictors — your age, how your prior labor unfolded, how this labor starts — aren't things you can engineer your way around. A lower predicted probability doesn't mean VBAC is off the table, and it isn't a reflection of anything you did wrong. Even a calculated probability of 40% still means a 4-in-10 chance of success, and plenty of women in that range go on to have smooth, successful VBACs.

Put Your Own Numbers In

Rather than guessing how these factors combine, our MFMU VBAC Calculator runs your age, BMI, obstetric history, and prior delivery details through the same clinical model many obstetricians use to counsel patients — giving you a personalized estimate to bring into your next appointment.

If you're weighing VBAC against a planned repeat cesarean, see VBAC vs. Repeat C-Section: How to Weigh Your Options. And if uterine rupture risk is the thing keeping you up at night, VBAC Uterine Rupture Risk: What 0.5% Really Means puts that number in perspective.