Vbac Success Rate Calculator

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VBAC Success Probability Calculator

Centimeters (cm) Inches (in)
Kilograms (kg) Pounds (lbs)
White / Other African American / Black Hispanic / Latina
No Yes (Either prior to or after C-section)
Non-Recurrent (e.g., Breech, Fetal Distress, Placenta Previa) Recurrent (Arrest of Dilation or Descent)
Estimated Success Probability
0%

Medical Disclaimer: This calculator uses the algorithm derived from the MFMU Network model. It provides a statistical estimation based on population data, not a personalized medical prediction. This tool is for informational purposes only and does not constitute medical advice. Always consult your obstetrician or healthcare provider for decisions regarding your birth plan.

Understanding Your VBAC Success Rate

Vaginal Birth After Cesarean (VBAC) is a safe option for many women who have previously undergone a cesarean delivery. The "Trial of Labor After Cesarean" (TOLAC) allows women to attempt a vaginal birth. Success rates vary based on individual medical history and demographic factors.

How This Calculator Works

This calculator utilizes a regression model similar to the widely cited Maternal-Fetal Medicine Units (MFMU) Network calculator. It analyzes specific coefficients that have been statistically shown to influence the likelihood of a successful vaginal delivery.

Key Factors Influencing Success

  • Maternal Age: Generally, younger maternal age is associated with slightly higher success rates, though successful VBACs occur frequently across all childbearing ages.
  • BMI (Body Mass Index): Calculated from your height and pre-pregnancy weight. A lower BMI typically correlates with a higher statistical probability of success, while a higher BMI may present additional challenges during labor.
  • Prior Vaginal Delivery: This is the single strongest predictor of success. If you have delivered vaginally before (either before your C-section or a successful VBAC since), your odds of success increase significantly.
  • Reason for Previous C-Section: The "indication" matters. If the C-section was performed for a non-recurrent reason (like a breech baby or placenta previa), the odds of a successful vaginal birth in the next pregnancy are higher than if the surgery was due to "arrest of labor" (the cervix stopped dilating or the baby stopped descending).

Interpreting the Results

The percentage generated represents the likelihood that a Trial of Labor (TOLAC) will result in a vaginal birth. For example, a result of 70% means that out of 10 women with a similar profile, approximately 7 would deliver vaginally, while 3 might require a repeat cesarean section.

What constitutes a "Good" Candidate?

There is no specific cutoff for attempting a TOLAC. However, the American College of Obstetricians and Gynecologists (ACOG) suggests that women with a calculated probability of at least 60-70% have the same probability of vaginal delivery as women having their first baby. Even with lower calculated probabilities, many providers support TOLAC after a thorough counseling session regarding risks and benefits.

Benefits vs. Risks

Choosing between a repeat C-section and a VBAC involves weighing benefits and risks:

  • Benefits of VBAC: No abdominal surgery, shorter recovery time, lower risk of infection, less blood loss, and easier bonding/breastfeeding initiation.
  • Risks of TOLAC: The primary risk is uterine rupture (occurring in roughly 0.5% to 0.9% of cases), which is an emergency situation requiring immediate surgical intervention.

Always discuss your specific medical history, future family planning desires, and risk tolerance with your healthcare provider.

function calculateVBAC() { // 1. Get Input Values var age = parseFloat(document.getElementById("vbacAge").value); var height = parseFloat(document.getElementById("vbacHeight").value); var heightUnit = document.getElementById("vbacHeightUnit").value; var weight = parseFloat(document.getElementById("vbacWeight").value); var weightUnit = document.getElementById("vbacWeightUnit").value; var race = document.getElementById("vbacRace").value; var history = document.getElementById("vbacHistory").value; var indication = document.getElementById("vbacIndication").value; // 2. Validation if (isNaN(age) || isNaN(height) || isNaN(weight)) { alert("Please enter valid numbers for Age, Height, and Weight."); return; } // 3. Normalize Units to Metric (Meters and Kilograms) var heightMeters = height; if (heightUnit === "in") { heightMeters = height * 0.0254; } else { heightMeters = height / 100; } var weightKg = weight; if (weightUnit === "lbs") { weightKg = weight * 0.453592; } // 4. Calculate BMI var bmi = weightKg / (heightMeters * heightMeters); // 5. Apply Coefficients (Based on standard MFMU Regression Model approximation) // Formula: Log(odds) = Intercept + (Coeff * Factor) // Constants derived from Grobman et al. var intercept = 3.303; // Base constant var ageCoeff = -0.033; var bmiCoeff = -0.051; var africanAmericanCoeff = -0.655; var hispanicCoeff = -0.626; var priorVaginalCoeff = 0.888; var recurrentIndicationCoeff = -0.745; // Arrest of dilation/descent var logOdds = intercept; // Add Age Factor logOdds += (ageCoeff * age); // Add BMI Factor logOdds += (bmiCoeff * bmi); // Add Race Factor if (race === "black") { logOdds += africanAmericanCoeff; } else if (race === "hispanic") { logOdds += hispanicCoeff; } // White/Other is the reference group (adds 0) // Add History Factor if (history === "yes") { logOdds += priorVaginalCoeff; } // Add Indication Factor if (indication === "arrest") { logOdds += recurrentIndicationCoeff; } // 6. Calculate Probability (Logistic Function) // Probability = e^logOdds / (1 + e^logOdds) var probability = Math.exp(logOdds) / (1 + Math.exp(logOdds)); var percent = probability * 100; // 7. Display Result var resultBox = document.getElementById("vbacResult"); var resultValue = document.getElementById("resultValue"); var resultText = document.getElementById("resultText"); resultBox.style.display = "block"; resultValue.innerHTML = percent.toFixed(1) + "%"; // Interpretation Text var interpretation = ""; if (percent >= 70) { interpretation = "This suggests a high likelihood of a successful vaginal delivery."; } else if (percent >= 50) { interpretation = "This suggests a moderate likelihood of success."; } else { interpretation = "The statistical model suggests a lower probability, but success is still possible."; } resultText.innerHTML = interpretation; }

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