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VBAC Calculator (Vaginal Birth After Cesarean Section)

Created by Dominika Śmiałek, MD, PhD candidate
Reviewed by Dominik Czernia, PhD and Jack Bowater
Based on research by
Grobman WA, Lai Y, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU). Development of a nomogram for prediction of vaginal birth after cesarean delivery.; Obstetrics & Gynecology; April 2007
Last updated: Sep 28, 2023


With this VBAC calculator (Vaginal Birth After Cesarean Section), you can estimate the chances of a successful vaginal birth, even if you've had a c-section in the past. In the article below, there are some explanations on what is VBAC, VBAC risk, and TOLAC (Trial of Labor After Cesarean Section) risk.

You can also check your due date with our due date calculator.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. All information on this website is for informational purposes only and is not intended to serve as a substitute for medical consultation. Always consult your results with a health care provider.

What is VBAC?

VBAC, which stands for vaginal birth after c-section (cesarean section), is a term used for women who have had a cesarean section in the past and have decided on a vaginal birth in the current pregnancy.

TOLAC, or trial of labor after cesarean section, describes all patients who have agreed to try a vaginal birth after a c-section, while VBAC is only those who have succeeded. This tool calculates the odds that TOLAC ends up as a vaginal delivery (VBAC probability).

The rate of C-sections has grown in the last century - in 2021, almost one-third of mothers in the US had a c-section.

What are indications for C-section?

There are various indications for cesarean section, both fetal and maternal.
Some of the maternal indications:

  • Herpes simplex or HIV infection;
  • Cardiac or pulmonary disease;
  • Cerebral aneurysm or arteriovenous malformation.

Some of the fetal indications:

  • Umbilical cord prolapse
  • Macrosomia
  • Congenital anomaly

Above we list only a couple of the indications for cesarean section. There are many more indications and contraindications and the decision should be made by the health care provider and the pregnant patient.

VBAC birth - what are the risks?

Pregnancy after a c-section might make you a little bit nervous, especially when making a decision: c-section vs vaginal birth. That's why you should discuss with your physician all of the pros and cons, whatever your choice.
One of the significant yet rare complications of VBAC delivery is a uterine rupture, where the uterus opens. Subsequent bleeding and the necessity of hysterectomy (uterus removal) might be needed. After a hysterectomy, it's impossible to conceive again.

What to choose - c-section vs vaginal birth

The final decision on the type of delivery should be made after the patient's discussion with her physician. There are some important factors, according to the Grobman model:

  1. Age - younger women are more likely to perform a vaginal birth after a c-section successfully.
  2. Ethnicity - being of Hispanic or AfroAmerican ethnicity decreases the chances.
  3. BMI - the lower the BMI (but still in a healthy range), the higher chances for a successful birth. Check your BMI with the BMI calculator.
  4. Vaginal birth in the past - increases chances.
  5. Vaginal birth in the past, but specifically AFTER a previous c-section - increases chances.
  6. Recurring indications for c-section (such as cephalopelvic disproportion, dystocia, failure to progress) - slightly decrease the chances of successful VBAC delivery.

Short introduction on how to calculate VBAC risks

In our VBAC calculator based on the Grobman model, you need to know: age, ethnicity, BMI from before pregnancy, and history of previous births. For BMI, you can either calculate the number yourself (check the BMI calculator for women) or put in your height and pre-pregnancy weight. Fill in all the fields and choose the correct options.

How to interpret the results?

  1. The first number is the probability of a successful VBAC delivery.
  2. Just below, you can find the VBAC score, calculated based on the results of your previous answers.

The VBAC calculator is based on a formula derived from the Development of a nomogram for prediction of vaginal birth after cesarean delivery.

VBAC calculator in practice

Let's take Judith, a 35-year-old mum-of-two, currently pregnant with her third baby. Her last delivery had to be a c-section due to pregnancy-induced hypertension and excessive weight gain. Take a moment how much weight you should gain during this period with our pregnancy weight gain calculator). This pregnancy after c-section is progressing fine. Now she is 37 weeks pregnant, and is discussing with her gynecologist the best option for delivery. The doctor suggested to take a chance and perform TOLAC. But, before that, Judith wants to know "what is VBAC?", "what are the chances of a successful VBAC birth?" and finally, "what are the VBAC risks?". To explain her odds, the gynecologist uses this VBAC calculator:

  • age: 35 years
  • ethnicity: White
  • BMI: 24.5
  • vaginal birth in the past: YES
  • vaginal birth since cesarean section: NO
  • recurring reason for cesarean delivery: NO

The result is: score: 65.3, probability: 86.04%.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

Dominika Śmiałek, MD, PhD candidate
Personal data
Age
years
Ethnicity
African American
Do you know your BMI?
Yes
Your BMI
Obstetrics history
Any prior vaginal delivery?
No
Recurring reason for cesarean delivery?
No
Results
VBAC Score (Grobman model):
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