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VBAC

VBAC: calculated with the published clinical method, with result interpretation. A reference tool that does not replace a doctor's advice.

ℹ Reference calculation based on the published method. It does not replace a clinical examination or a doctor's decision.

VBAC

Woman's ageyears
Pre-pregnancy weightkg
Woman's heightcm
Obstetric history (1 = no prior vaginal birth, 2 = vaginal birth only before the cesarean, 3 = prior VBAC)
Prior cesarean was for arrest of dilation or descent (1 = yes)
Chronic hypertension treated with medication (1 = yes)
Chance of vaginal birth after cesarean (VBAC)
59.6283%
MFMU 2021 model without race and ethnicity (Grobman et al., Am J Obstet Gynecol 2021): P = eʷ / (1 + eʷ)Only for a singleton cephalic pregnancy at 37 weeks or more with one prior low-transverse cesareanPer Grobman et al. (AJOG 2009), cited by ACOG, with a VBAC chance of at least 60–70% maternal morbidity with a trial of labor is no higher than with a planned repeat cesarean. Decide together with your doctorVBAC: calculated with the published clinical method, with result interpretation. A reference tool that does not replace a doctor's advice.
History used in the model
No prior vaginal birth
Linear predictor w
0.39
Chance of repeat cesarean during a trial of labor
40.4%
Pre-pregnancy BMI (for reference)
29.2
Average VBAC rate in the MFMU study
73.9%

More about: VBAC

What it calculates

The “VBAC” calculator computes Chance of vaginal birth after cesarean (VBAC) in % from 6 parameters: woman's age (years), pre-pregnancy weight (kg), woman's height (cm), obstetric history (1 = no prior vaginal birth, 2 = vaginal birth only before the cesarean, 3 = prior vbac), prior cesarean was for arrest of dilation or descent (1 = yes), chronic hypertension treated with medication (1 = yes).

Used by professionals and patients to assess health metrics, dosages, and risks.

Example calculation

With parameters Woman's age = 30 years, Pre-pregnancy weight = 71 kg, Woman's height = 156 cm, Obstetric history (1 = no prior vaginal birth, 2 = vaginal birth only before the cesarean, 3 = prior VBAC) = 1, Prior cesarean was for arrest of dilation or descent (1 = yes) = 0, Chronic hypertension treated with medication (1 = yes) = 0 the result is 59.63 % (MFMU 2021 model without race and ethnicity (Grobman et al., Am J Obstet Gynecol 2021): P = eʷ / (1 + eʷ)).

How to use

  1. Enter woman's age, pre-pregnancy weight, woman's height, obstetric history (1 = no prior vaginal birth, 2 = vaginal birth only before the cesarean, 3 = prior vbac), prior cesarean was for arrest of dilation or descent (1 = yes) and chronic hypertension treated with medication (1 = yes) — each field above is adjustable with a slider.
  2. Chance of vaginal birth after cesarean (VBAC) (%) is calculated automatically as you type.
  3. Check the worked example below to see the formula applied to real numbers.
  4. Copy the result or bookmark this calculator.

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FAQ

How is BMI calculated?
BMI = weight (kg) / height (m)². Example: 70 kg / (1.75 m)² = 22.9. The WHO normal range is 18.5–24.9; below that is underweight, 25–29.9 is overweight, and 30+ is obese.
Is BMI accurate for everyone?
No. BMI does not distinguish muscle from fat, so athletes may show a high BMI with low body fat. It is also less reliable for teenagers, pregnant people, older adults, and very tall or short individuals.
What are the BMI categories?
Underweight: below 18.5. Normal: 18.5–24.9. Overweight: 25–29.9. Obese class I: 30–34.9; class II: 35–39.9; class III: 40+.
What is a better measure than BMI?
Body fat percentage, waist-to-height ratio (aim for under 0.5), and waist circumference give a clearer picture of health than BMI alone.

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