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VBAC Success Calculator (MFMU 2021, without race and ethnicity)

Predicts the chance of vaginal birth after one prior low-transverse cesarean in a term trial of labor, using information available at the first prenatal visit and no race or ethnicity (MFMU Network, Grobman 2021; AUC 0.75). Taller height and any prior vaginal birth (especially a prior VBAC) raise the chance; older age, heavier pre-pregnancy weight, a prior arrest-disorder cesarean and treated chronic hypertension lower it.

Age (years)
Pre-pregnancy weight (kg or lb)
Height (cm or m or in)
Prior vaginal birth: No prior vaginal birth; Vaginal birth only before the prior cesarean; Prior VBAC (vaginal birth after the cesarean)
Prior cesarean for arrest of dilation or descent (incl. failed induction) (yes/no, +1)
Chronic hypertension treated with medication (yes/no, +1)

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Interpretation

Result	Meaning
≥ 70%	Favourable; ACOG notes that with ≥60–70% predicted success, TOLAC morbidity is equal to or lower than repeat cesarean
50–69%	Moderate
< 50%	Lower chance; TOLAC morbidity likely higher than elective repeat cesarean

Formula

P(VBAC) = e^w / (1 + e^w); w = −5.952 − 0.023·age − 0.024·pre-pregnancy weight (kg) + 0.056·height (cm) − 0.597·arrest indication + 0.868·vaginal birth only before prior cesarean + 1.869·prior VBAC − 0.966·treated chronic hypertension.

Clinical pearls

Valid only for one prior low-transverse cesarean, a singleton cephalic fetus and labor at ≥37 weeks; not for prior classical incision, myomectomy or ≥2 prior cesareans.
This 2021 model replaces the 2007 MFMU calculator, which used race and ethnicity. A separate 2024 MFMU model uses admission-for-delivery information.
Probability bands here are descriptive; the predicted percentage is a counselling aid, not a cut-off for offering TOLAC.

Examples

vbac 30 yo 70 kg 165 cm no prior vaginal birth, prior cs for breech VBAC calculator: 35 years, 100 kg, 160 cm, prior c-section for arrest of dilation, treated chronic hypertension chance of vbac for a 28 year old, 60 kg, 170 cm, had a VBAC before

FAQ

Why was race removed from the VBAC calculator?

The 2007 MFMU calculator assigned lower VBAC chances to Black and Hispanic patients. The 2021 refit without race or ethnicity had the same accuracy (AUC 0.75).

What VBAC probability is considered good?

ACOG notes that when the chance of VBAC is at least 60–70%, maternal morbidity with TOLAC is equal to or less than with an elective repeat cesarean.

Evidence

Grobman WA et al. Prediction of vaginal birth after cesarean delivery in term gestations: a calculator without race and ethnicity. Am J Obstet Gynecol 2021;225:664.e1–7.

Pediatrics & Obstetrics · Reviewed 2026-10-14 · Methodology