VBAC Success Calculator (Grobman, race-free 2021)
Grobman nomogram predicting the probability of a successful vaginal birth after cesarean (VBAC) from maternal age, BMI, prior delivery history, and clinical factors.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Maternal age
- 30 years
- Pre-pregnancy weight
- 80 kg
- Height
- 165 cm
- Prior vaginal delivery history
- Prior VBAC (vaginal delivery after the cesarean) — +1.869
Result: Predicted VBAC success probability 92.7%.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Use
- the race/ethnicity-free 2021 successor to the Flamm score (uses weight + height, not BMI). A counseling aid, not a delivery-mode order.
What you enter
- Maternal age
- Pre-pregnancy weight
- Height
- Prior vaginal delivery history
- Prior cesarean for an arrest disorder
- Treated chronic hypertension
How this is calculated
- Model
- logit = −5.952 − 0.023·age − 0.024·weight(kg) + 0.056·height(cm) − 0.597·arrest + 0.868·prior vaginal + 1.869·prior VBAC − 0.966·treated chronic HTN; probability = e^logit/(1+e^logit).
Grobman WA, Sandoval G, Rice MM, et al. Prediction of vaginal birth after cesarean delivery in term gestations: a calculator without race and ethnicity. Am J Obstet Gynecol. 2021;225(6):664.e1-664.e7. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.