Non-Recurrent (e.g., Breech, Fetal Distress)
Recurrent (e.g., Arrest of Dilation/Labor)
Predicted Chance of Successful VBAC:
–%
Medical Disclaimer: This calculator uses logic based on the MFMU Network model to estimate the likelihood of a successful vaginal birth after cesarean (VBAC). This tool is for informational purposes only and does not constitute medical advice. Always consult your obstetrician for personalized risk assessment.
function calculateTOLAC() {
// 1. Get input values
var age = parseFloat(document.getElementById("maternalAge").value);
var height = parseFloat(document.getElementById("maternalHeight").value);
var weight = parseFloat(document.getElementById("maternalWeight").value);
var race = document.getElementById("raceEthnicity").value;
var priorVaginal = parseInt(document.getElementById("priorVaginal").value);
var indication = document.getElementById("indication").value;
// 2. Validation
if (isNaN(age) || isNaN(height) || isNaN(weight)) {
alert("Please enter valid numbers for Age, Height, and Weight.");
return;
}
// 3. Calculate BMI
// Formula: 703 x weight (lbs) / [height (in)]^2
var bmi = (703 * weight) / (height * height);
// Cap BMI at 50 for realistic calculation limits if needed,
// though standard formula applies generally. Let's keep it raw but warn if extreme.
// 4. Coefficients based on MFMU Model (Approximate values for web implementation)
// Intercept
var logOdds = 3.302;
// Age Coefficient (-0.034)
logOdds += (-0.034 * age);
// BMI Coefficient (-0.029)
logOdds += (-0.029 * bmi);
// Race/Ethnicity Coefficients
if (race === "black") {
logOdds += (-0.675);
} else if (race === "hispanic") {
logOdds += (-0.678);
}
// White/Other is the baseline (0)
// Prior Vaginal Delivery Coefficient (+0.916)
if (priorVaginal === 1) {
logOdds += 0.916;
}
// Recurring Indication Coefficient (-0.635)
// Recurring means "Arrest of dilation" or "Arrest of descent"
if (indication === "recurring") {
logOdds += (-0.635);
}
// 5. Convert Log Odds to Probability
// Probability = e^x / (1 + e^x)
var probability = Math.exp(logOdds) / (1 + Math.exp(logOdds));
var percentage = probability * 100;
// 6. Display Result
var resultDiv = document.getElementById("tolacResult");
var resultText = document.getElementById("resultPercent");
var bmiText = document.getElementById("bmiDisplay");
resultDiv.style.display = "block";
resultText.innerHTML = percentage.toFixed(1) + "%";
bmiText.innerHTML = "Calculated BMI: " + bmi.toFixed(1);
// Scroll to result
resultDiv.scrollIntoView({behavior: "smooth"});
}
Understanding Your TOLAC Success Rate
A Trial of Labor After Cesarean (TOLAC) is the attempt to have a vaginal birth (VBAC) after having undergone a cesarean section in a previous pregnancy. For many expectant mothers, a successful VBAC offers shorter recovery times, lower infection risks, and fewer complications compared to a repeat C-section. However, not everyone is an ideal candidate.
This calculator utilizes data derived from the Maternal-Fetal Medicine Units (MFMU) Network to estimate the probability of a successful vaginal delivery. It takes into account specific maternal factors that have been statistically shown to influence labor outcomes.
Key Factors Influencing VBAC Success
Several clinical variables significantly impact the likelihood of a successful TOLAC:
Prior Vaginal Delivery: This is the strongest predictor of success. Women who have had at least one vaginal birth (either before or after their C-section) have significantly higher success rates, often exceeding 85%.
Reason for Previous C-Section: The "indication" for the prior surgery matters. If the C-section was performed for a non-recurring issue (like a breech baby or fetal distress), the chances of success are higher than if it was performed because labor stalled (arrest of dilation or descent).
Maternal Body Mass Index (BMI): Lower BMI is generally associated with higher success rates. As BMI increases, the likelihood of requiring a repeat C-section during labor increases slightly.
Maternal Age: Younger maternal age is statistically associated with slightly higher success rates.
Interpreting Your Score
The result provided is a statistical probability expressed as a percentage.
High Probability (>70%): Indicates a strong likelihood of success, comparable to women laboring for the first time.
Moderate Probability (40-69%): Indicates a reasonable chance of success, though the risk of needing a repeat C-section during labor is higher.
Lower Probability (<40%): While success is still possible, the likelihood of a failed trial of labor is statistically higher.
Risks of TOLAC vs. Repeat C-Section
The decision to attempt a TOLAC involves balancing risks. A successful VBAC is generally the safest outcome for mother and baby. However, an unsuccessful TOLAC (requiring an emergency C-section during labor) carries higher risks of complications, such as infection or uterine rupture, compared to a scheduled repeat C-section.
Uterine rupture is the most serious risk associated with TOLAC, occurring in approximately 0.5% to 0.9% of cases with a standard low transverse incision. Because of this, TOLAC should always be attempted in a facility capable of performing an emergency cesarean delivery.
Note: This calculator is designed for women with one prior low-transverse cesarean section and a singleton pregnancy (one baby). It is not applicable for women with vertical incisions, multiple prior C-sections, or twin pregnancies.