Obstetrics

VBAC Probability Without Race or Ethnicity calculator

Enter the published formula inputs below to calculate and interpret this score.

Clinical inputs

Maternal age

years

Allowed range: 15–55 years

Pre-pregnancy weight

Allowed range: 77.16–396.83 lb

Height

Allowed range: 55.12–78.74 in

Prior cesarean for arrest of labor

Yes means the prior cesarean was for arrest of dilation or descent. That term subtracts 0.597.

Earlier vaginal birth

A vaginal birth only before the cesarean adds 0.868. A vaginal birth after the cesarean adds 1.869. The article treats these as separate histories.

Treated chronic hypertension

Yes means medication-treated chronic hypertension. That term subtracts 0.966.

Result

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Primary source

Grobman WA et al. Prediction of vaginal birth after cesarean delivery in term gestations: a calculator without race and ethnicity. Am J Obstet Gynecol. DOI: 10.1016/j.ajog.2021.05.021. PMID: 34043983. Predicted percent = 100 × exp(w) / (1 + exp(w)), where w = −5.952 − 0.023 × age in years − 0.024 × pre-pregnancy weight in kg + 0.056 × height in cm − 0.597 if the prior cesarean was for arrest of dilation or descent + 0.868 if the only prior vaginal birth was before the cesarean + 1.869 if there was a vaginal birth after the cesarean − 0.966 if chronic hypertension was treated with medication. Each yes/no term is 1 or 0. The two vaginal-history terms are mutually exclusive in the article's wording. Table 3 prints 95.6%, 90.5%, 77.7%, 77.2%, 73.4%, 63.3%, 59.4%, 55.4%, 48.7%, 44.6%, 35.8%, and 32.1% for its 12 scenarios. The printed 3-decimal equation gives 95.7, 90.5, 77.9, 77.4, 73.8, 63.4, 59.6, 55.7, 48.9, 44.8, 36.0, and 32.4 for those same inputs. The reported number follows the printed equation. The article does not set a percent at which a trial of labor should or should not be chosen. (2021)

Scope: Term singleton cephalic pregnancy with one prior low-transverse cesarean, using facts known at the first prenatal visit. The percent is the chance of vaginal birth if a trial of labor is undertaken.

Last reviewed 2026-10-17

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Professional use only

For qualified clinicians. Independently verify inputs, calculations, source guidance, and applicability before any clinical action. This calculator does not replace clinical judgment.

Source: Grobman WA et al. Prediction of vaginal birth after cesarean delivery in term gestations: a calculator without race and ethnicity. Am J Obstet Gynecol. DOI: 10.1016/j.ajog.2021.05.021. PMID: 34043983. Predicted percent = 100 × exp(w) / (1 + exp(w)), where w = −5.952 − 0.023 × age in years − 0.024 × pre-pregnancy weight in kg + 0.056 × height in cm − 0.597 if the prior cesarean was for arrest of dilation or descent + 0.868 if the only prior vaginal birth was before the cesarean + 1.869 if there was a vaginal birth after the cesarean − 0.966 if chronic hypertension was treated with medication. Each yes/no term is 1 or 0. The two vaginal-history terms are mutually exclusive in the article's wording. Table 3 prints 95.6%, 90.5%, 77.7%, 77.2%, 73.4%, 63.3%, 59.4%, 55.4%, 48.7%, 44.6%, 35.8%, and 32.1% for its 12 scenarios. The printed 3-decimal equation gives 95.7, 90.5, 77.9, 77.4, 73.8, 63.4, 59.6, 55.7, 48.9, 44.8, 36.0, and 32.4 for those same inputs. The reported number follows the printed equation. The article does not set a percent at which a trial of labor should or should not be chosen. (2021)

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Clinical inputs

Maternal age (years)Accepted range: 15 to 55
Pre-pregnancy weight (kg)Accepted range: 35 to 180
Height (cm)Accepted range: 140 to 200
Prior cesarean for arrest of labor
Earlier vaginal birth
Treated chronic hypertension

Primary source

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