VBAC Calculator (Vaginal Birth After Cesarean Section)

Written by Great Medico

Updated September 24, 2026 •2 min read

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A VBAC percentage is useful only when its model and limits stay visible. VBAC Calculator (Vaginal Birth After Cesarean Section) applies the variables in this plugin to estimate the chance of vaginal birth after a prior cesarean.

What this calculator does

VBAC Calculator (Vaginal Birth After Cesarean Section) uses Age, Ethnicity, Pre-pregnancy BMI, Prior vaginal delivery, and Recurring indication for previous cesarean to calculate predicted VBAC success percentage. It is built around the exact fields displayed in this plugin rather than a generic version of the topic. VBAC prediction is a counseling aid rather than a pass/fail test. Prior obstetric history, the reason for the previous cesarean, current pregnancy factors, local resources, and patient preferences all matter alongside any calculated percentage.

How to use it

Enter or select Age, Ethnicity, Pre-pregnancy BMI, Prior vaginal delivery, and Recurring indication for previous cesarean. Use the units offered by the calculator and choose the option that matches the actual clinical or timing situation. Check date entries and laboratory units before relying on the output. For paired dates or serial measurements, keep them within the same menstrual cycle, pregnancy, or treatment episode as the calculator requires.

How the calculation works

This implementation uses the older logistic VBAC model encoded in the plugin: an intercept plus coefficients for maternal age, BMI, race/ethnicity category, prior vaginal delivery, and a recurrent indication for the previous cesarean. The logistic transformation converts that linear score into a predicted percentage of VBAC success.

Example

Using the sample values prefilled in this calculator, the primary result is 74.95 % (Predicted VBAC success). This worked example shows how the plugin’s own default inputs flow through the implemented method; replace them with the correct patient, laboratory, imaging, or personal values before interpreting a result.

How to interpret the result

The percentage is the predicted VBAC-success estimate produced by the older model encoded in this plugin. It is one counseling input, not a pass/fail threshold for TOLAC, and the race/ethnicity terms in this legacy equation limit its appropriateness for current decision-making.

Limitations and notes

This calculator contains the older race/ethnicity coefficients. ACOG advises against using race/ethnicity in VBAC prediction and notes that the newer NICHD calculator removes those variables. A VBAC estimate should support shared decision-making and must not be used as a barrier to offering TOLAC to an otherwise appropriate patient.