What success rate is considered good enough for TOLAC?

There is no universal go/no-go cutoff. The number is one counseling input, and the decision still depends on clinical eligibility, uterine-scar history, emergency cesarean capability, and patient preferences.

What is uterine rupture risk?

With one prior low-transverse cesarean, uterine rupture risk during TOLAC is roughly 0.5% to 0.7%. Risk is higher with classical scars, multiple prior cesareans, short inter-delivery intervals, and some induction methods.

Does induction of labor affect VBAC success?

Yes. Induction can lower VBAC success compared with spontaneous labor, and induction planning should follow current obstetric guidance for TOLAC candidates.

Why does the model include race?

The legacy published model included race-adjusted coefficients, which is one reason the calculator should be treated as a historical counseling model rather than a stand-alone decision rule. Many clinicians now prefer counseling approaches that do not let race-based coefficients decide access to TOLAC.

What if I have had two prior cesareans?

This model was primarily developed for patients with one prior cesarean. TOLAC after two prior cesareans needs separate counseling and institution-specific capability review.

Can this calculator be used before labor?

Yes, but the estimate is rougher before admission because cervical findings are not yet known. Prenatal counseling should still focus on the full obstetric context rather than the model alone.

VBAC Risk Score Calculator

Estimate VBAC success with a legacy Grobman-style counseling model, framed as discussion support rather than a stand-alone eligibility rule.

⚠️ Medical Disclaimer: This page reflects a legacy Grobman-style VBAC counseling model. It is a discussion aid only and should not be used by itself to offer, deny, or pressure a patient toward TOLAC or repeat cesarean.

Age

years

Height

Weight at delivery

Legacy model race/ethnicity field

Prior vaginal delivery (any)

Prior successful VBAC

Indication for prior cesarean

Cervical dilation at admission

Cervical effacement at admission

The published legacy nomogram included race-adjusted coefficients. Treat the output as counseling context rather than as a stand-alone access rule for TOLAC.

<50%

50-70%

≥70%

▼

Predicted VBAC Success

83.2%

Higher Predicted Success

✗ Prior vaginal delivery

✗ Prior VBAC

✓ Non-recurring indication

✓ BMI <30

✓ Age <35

VBAC Success Rate

83.2%

Higher Predicted Success

BMI at Delivery

29.4

Lower BMI is generally more favorable in the legacy model

Uterine Rupture Risk

~0.5%

Background context for one prior low-transverse cesarean

Failed TOLAC Risk

16.8%

Emergency cesarean may still be needed if TOLAC is attempted

Counseling Use

Shared decision support

Legacy model estimate for counseling, not a go/no-go rule

Model Scope

Legacy counseling model

Includes legacy race-adjusted coefficients and should not be treated as a stand-alone eligibility rule

Factor	Effect on Predicted Success	General Direction
Prior vaginal delivery	Improves predicted success	Favorable history factor
Prior successful VBAC	Strongly improves predicted success	One of the strongest favorable factors
Non-recurring prior indication	Improves predicted success	Often more favorable than recurring arrest/CPD patterns
More favorable cervix	Improves predicted success	Admission cervical findings matter in the labor model
Higher BMI	Reduces predicted success	Model effect, not a stand-alone exclusion
Older maternal age	Reduces predicted success	Modest downward model effect
Recurring prior indication	Reduces predicted success	Needs careful individualized counseling
No prior vaginal delivery	Reduces predicted success	Common lower-success feature in the nomogram

Predicted Success	Reading	Counseling Points
≥70%	Higher modeled success	Often supports a favorable counseling discussion if the patient is otherwise an appropriate TOLAC candidate
50-70%	Intermediate modeled success	Shared decision-making is especially important, including facility capability and patient priorities
<50%	Lower modeled success	Signals a tougher counseling conversation, but does not by itself exclude TOLAC

Planning notes, formulas, and examples

About the VBAC Risk Score Calculator

This page estimates VBAC success with a Grobman-style counseling model for trial of labor after cesarean (TOLAC). It uses age, BMI, delivery history, prior cesarean indication, and cervical findings to generate a rough success probability that can help structure counseling.

The key limitation is that the legacy published model includes race-adjusted coefficients and was designed as a counseling aid, not as a gatekeeping rule. Because of that, the most honest way to read this page is as a legacy decision-support model rather than as a definitive answer about whether a patient should or should not attempt TOLAC.

Use the output only in the context of clinician counseling, obstetric history, uterine-scar details, facility capability, and patient preferences.

When This Page Helps

A VBAC counseling model can be useful when the discussion has become too abstract and the team needs a rough estimate of how favorable the labor history and current presentation look.

Its value is in structuring conversation. It should not override clinical eligibility, patient goals, or a modern individualized discussion of uterine rupture risk, emergency cesarean access, and other pregnancy-specific factors.

How to Use the Inputs

Enter maternal age and body measurements for BMI calculation.
Select the legacy model race/ethnicity field only if you are intentionally reproducing that published nomogram.
Indicate prior vaginal delivery, prior VBAC, and the prior cesarean indication.
Enter cervical dilation and effacement if the patient is in labor.
Review the predicted success rate as a counseling aid rather than a stand-alone recommendation.

Formula used

MFMU VBAC Prediction Model (simplified Grobman):
Logit = 3.766 - (0.039 × age) - (0.067 × BMI)
  - 0.671 (if African American)
  - 0.468 (if Hispanic)
  + 0.888 (if prior vaginal delivery)
  + 1.003 (if prior VBAC)
  + 0.446 (if non-recurring indication)
  + 0.105 × cervical dilation (cm)
  + 0.017 × effacement (%)

Probability = 1 / (1 + e^(-logit))

Example Calculation

Result: Predicted VBAC Success: 78.3%

This profile has several factors that improve modeled success, including prior vaginal delivery, a non-recurring prior cesarean indication, and a favorable cervix. The result should be used to support counseling, not to substitute for the full TOLAC eligibility discussion or to impose a numeric cutoff.

Tips & Best Practices

Treat the result as a counseling aid rather than a numeric permission slip.
Prior successful VBAC is one of the strongest favorable factors in the legacy model.
Non-recurring indications usually carry better modeled odds than recurring indications.
Higher BMI lowers predicted success in the model, but it is not a stand-alone reason to deny TOLAC.
TOLAC requires immediate cesarean capability and an appropriate obstetric setting.
Discuss both outcomes with the patient: the potential benefits of successful VBAC and the risks of failed TOLAC requiring emergency cesarean.

What the Page Is Good For

This page is useful when the counseling discussion needs a rough legacy-model estimate of VBAC success instead of an unstructured impression.

What It Does Not Do

It does not determine eligibility for TOLAC, and it should not be used to deny TOLAC because of a single number. The race-adjusted coefficients in the historical model are one reason to read it cautiously.

Best Use

Use it as one part of a shared decision-making conversation that also covers scar type, prior birth history, facility capability, induction plans, and patient values.

Sources & Methodology

Last updated: March 27, 2026

Methodology

This page reproduces a legacy Grobman-style VBAC counseling model that estimates the probability of successful vaginal birth after cesarean from age, BMI, delivery history, prior cesarean indication, and cervical findings. It is intentionally framed as a counseling aid rather than a stand-alone eligibility rule.

Because the historical model included race-adjusted coefficients, the output should be read cautiously and should not be used to offer or deny TOLAC by itself. Modern counseling still depends on the broader obstetric picture, uterine-scar history, facility capability, and patient preferences.

Sources

Development of a nomogram for prediction of vaginal birth after cesarean delivery (PubMed / Obstetrics & Gynecology) — Original Grobman VBAC prediction model publication.
Counseling Regarding Approach to Delivery After Cesarean and the Use of a Vaginal Birth After Cesarean Calculator (American College of Obstetricians and Gynecologists) — ACOG practice advisory emphasizing that VBAC calculators should support counseling rather than deny TOLAC.
MFMU Network VBAC Calculator (NICHD / MFMU Network) — Historical context for the published VBAC calculator lineage.

Frequently Asked Questions

There is no universal go/no-go cutoff. The number is one counseling input, and the decision still depends on clinical eligibility, uterine-scar history, emergency cesarean capability, and patient preferences.