Important Medical Disclaimer: This tool is based on clinical statistical models (similar to the MFMU network) but is for educational purposes only. It cannot predict your specific outcome. Birth decisions should only be made in consultation with your OB-GYN or midwife.
Understanding the VBAC Calculator
A VBAC (Vaginal Birth After Cesarean) is a clinical option for many people who have previously given birth via cesarean delivery. Choosing to attempt a vaginal birth after a previous C-section is medically referred to as a Trial of Labor After Cesarean (TOLAC). If the labor results in a vaginal birth, it is called a VBAC.
How Success is Calculated
Medical researchers have identified several factors that statistically influence the success rate of a TOLAC. Our calculator uses a weighted algorithm based on these common clinical variables:
Prior Vaginal Delivery: This is the strongest predictor of success. If you have had a vaginal birth before, your success rate increases significantly.
Reason for Previous C-section: If your previous C-section was for a "non-recurring" reason like the baby being breech (head up), your chances are higher than if the C-section was due to "failure to progress" (arrest of dilation).
Maternal BMI: Statistics show that a lower BMI is generally associated with a higher likelihood of a successful TOLAC.
Age: Generally, younger maternal age is associated with slightly higher success rates in various clinical models.
Interpreting Your Results
Most clinical studies suggest that the overall success rate for TOLAC is between 60% and 80%. If your calculated score is in this range or higher, many providers consider you a strong candidate for VBAC. If your score is lower, it doesn't mean a VBAC is impossible, but it may involve different risks that you should discuss with your surgical team.
Frequently Asked Questions
What are the benefits of VBAC?
Benefits include avoiding major abdominal surgery, lower risk of infection, shorter recovery time, and decreased risk of complications in future pregnancies (such as placenta previa or accreta).
What are the risks of TOLAC?
The most serious, though rare, risk is uterine rupture (less than 1% in most cases with a single low-transverse scar). If a TOLAC is unsuccessful, an emergency C-section may be required, which carries more risk than a planned repeat C-section.
Can I have a VBAC with two previous C-sections?
Yes, many clinical guidelines state that a TOLAC after two previous low-transverse cesarean births is a reasonable option for many women, though success rates and risks may vary.
function calculateVbacProb() {
var age = parseFloat(document.getElementById('maternalAge').value);
var bmi = parseFloat(document.getElementById('maternalBmi').value);
var reason = document.getElementById('cSectionReason').value;
var priorVaginal = document.getElementById('priorVaginal').checked;
var priorVbac = document.getElementById('priorVbac').checked;
var resultBox = document.getElementById('vbacResultBox');
var resultDisplay = document.getElementById('vbacPercentage');
var interpretation = document.getElementById('vbacInterpretation');
// Validation
if (isNaN(age) || isNaN(bmi)) {
alert("Please enter valid numbers for age and BMI.");
return;
}
// Base success rate
var probability = 75.0;
// Adjust for age (Roughly -0.5% per year over 30)
if (age > 30) {
probability -= (age – 30) * 0.5;
} else if (age 25) {
probability -= (bmi – 25) * 1.2;
} else if (bmi 95) probability = 95;
if (probability = 75) {
interpretation.innerHTML = "You have a high statistical likelihood of a successful vaginal birth.";
} else if (probability >= 60) {
interpretation.innerHTML = "You are a good candidate for TOLAC. Discuss the plan with your provider.";
} else {
interpretation.innerHTML = "Your success rate is lower than average; discuss risks and benefits carefully with your doctor.";
}
}