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: Jan 04, 2023

If you thought that - once a C-section, always a C-section, you were wrong! With this VBAC calculator (Vaginal Birth After Cesarean Section), you will quickly know your 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 and why you should even consider a VBAC birth an option.

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

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 your TOLAC will end up as a vaginal delivery (VBAC probability). There are still many hospitals that don't support VBAC due to many maternal health-related reasons.

The rate of C-sections has grown in the last century - one-third of mothers in the US and 80-90% (!) of mothers visiting private clinics in Brazil have decided to have a c-section. Choosing between a c-section or a vaginal birth is not the easiest one. Doctors claim that natural birth is beneficial for the child due to natural immune system stimulation and hormonal changes. Also, the mother doesn't have to undergo surgery, with results in scarring, bleeding, and infections. What's more, she can go home earlier after birth and will have fewer issues breastfeeding. Not to forget the financial side - for a c-section, you need a surgical ward, anesthesiologist, and longer hospitalization.

What are indications for C-section?

Cesarean sections are advisable if vaginal birth is considered too risky. A physician will schedule a c-section when:

  • There is more than one baby expected.
  • The baby is huge compared to the size of the mother's pelvis.

As for maternal reasons, there are:

  • Diabetes.
  • Hypertension
  • Infection, transmittable during birth (genital herpes, HIV). Some of the transmissions can be prevented by giving the mother antibiotics before birth and therefore allowing vaginal delivery.

Not to forget the last indication - the mother's wish due to fear of pain or any other.

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. If there are no serious contraindications, vaginal birth after a c-section brings fewer complications than repetitive cesarean sections.

What to choose - c-section vs vaginal birth

The final decision on the type of delivery should be made after the mother's discussion with her physician. There are some factors that make you eligible for vaginal birth:

  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 - odds go up even more.
  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, all you need to know is a couple of facts, as mentioned before: Your 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 option and then... receive the results instantaneously:

  1. The first number is the probability of a successful VBAC delivery - it is the chance that your TOLAC will be without any complications nor the need to perform a c-section. The probability is calculated from the logistic regression model.
  2. Just below, you can find the VBAC score, calculated based on the results of your previous answers. Each answer is calculated from a specific number of points.

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 (a nonrecurring indication) 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
African American
Do you know your BMI?
Your BMI
Obstetrics history
Any prior vaginal delivery?
Recurring reason for cesarean delivery?
VBAC Score:
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