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MFMU VBAC Calculator

Estimate your probability of a successful Vaginal Birth After Cesarean using the clinical MFMU/NICHD model.

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Obstetric History

Why did you have your prior C-Section?
Probability of Successful VBAC
66.9%
Moderate Probability of Success
Calculated BMI: 26.6
Medical Disclaimer: This calculator uses the updated race-neutral MFMU (Maternal-Fetal Medicine Units) Network model to estimate the probability of a successful Vaginal Birth After Cesarean (VBAC). A high probability does not guarantee success, and a low probability does not mean VBAC is impossible. Always discuss your birthing options and surgical risks with your obstetrician.

Last updated: August 2026

Calculating Your VBAC Odds with the MFMU Model

If you have had a c-section in the past, you may be wondering if you are a good candidate for a Vaginal Birth After Cesarean (VBAC) for your current pregnancy. While the phrase "once a c-section, always a c-section" was medical gospel decades ago, it is completely outdated today.

Our VBAC Calculator is based on the updated, race-neutral MFMU (Maternal-Fetal Medicine Units) Network model — sometimes referred to as the "NICHD VBAC calculator" since it was developed through NICHD-funded research. It's the same model many obstetricians reference when counseling patients on delivery options. It currently uses five of the model's six factors; see the FAQ below on chronic hypertension for the one it doesn't yet capture.

A note on accuracy: This tool estimates 5 of the 6 factors in the official MFMU model (it omits chronic hypertension). If you're on medication for chronic hypertension, your real probability is somewhat lower than the number shown here. This calculator is a starting point for a conversation with your OB or midwife — not a diagnosis or a substitute for individualized clinical counseling.

How the MFMU VBAC Calculator Works

The model takes a handful of inputs from your obstetric and physical history and converts them into a single probability — your estimated percent chance of a successful vaginal delivery if you attempt a Trial of Labor After Cesarean (TOLAC). Enter your details in the tool above and you'll get an instant, personalized estimate rather than a generic population statistic.

Factors That Affect VBAC Success

The mathematical model uses several key pieces of your obstetric and physical history to calculate your odds of success:

  • Prior Vaginal Delivery: This is the strongest predictor of a successful VBAC. If your body has successfully delivered a baby vaginally in the past (either before or after your c-section), your odds of success skyrocket.
  • Reason for Prior C-Section: Why did you have your last c-section? If it was for a one-time issue like a breech baby or fetal distress, your odds of a successful VBAC are very high. If it was for "Failure to Progress" (you were stuck at 6cm dilated for hours), your odds are slightly lower, but a VBAC is absolutely still possible.
  • Maternal Age & BMI: Younger age and lower Body Mass Index (BMI) at the time of delivery generally correlate with higher VBAC success rates.

What is a "Good" Score?

According to ACOG, a calculated probability greater than 60-70% means you have roughly the same chance of a successful vaginal delivery as a first-time mother. However, even if your calculated probability is 40%, you still have a 4 in 10 chance of success. Many women with "low" scores go on to have incredibly smooth, successful VBACs.

Related Reading

Frequently Asked Questions

The MFMU (Maternal-Fetal Medicine Units) Network VBAC calculator is a clinical prediction tool developed through NICHD-funded research and used by obstetricians to estimate a patient's probability of a successful VBAC. It's sometimes called the 'NICHD VBAC calculator' or 'MFMU VBAC calculator' interchangeably — they refer to the same underlying model.
VBAC stands for Vaginal Birth After Cesarean. It refers to a successful vaginal delivery in a woman who has previously had a baby delivered by c-section.
For the vast majority of women with one prior low-transverse c-section, attempting a VBAC (known as a Trial of Labor After Cesarean, or TOLAC) is considered safe and is recommended by the American College of Obstetricians and Gynecologists (ACOG). However, there is a small risk of uterine rupture, which is why it should be discussed with your doctor.
The original 2007 version used race and ethnicity as inputs, which research showed systematically produced lower predicted probabilities for Black and Hispanic patients without a biological basis, contributing to inequitable counseling and higher c-section rates in those groups. The 2021 update removed these factors.
Not quite. The official 2021 model uses six factors: age, BMI, prior vaginal delivery, prior VBAC, the reason for your prior c-section, and whether you have chronic hypertension requiring medication. This tool currently captures the first five but does not yet factor in chronic hypertension, so if that applies to you, treat the result as a slight overestimate and raise it directly with your provider.
A lower score means a somewhat higher statistical chance of needing a repeat c-section, but it does not mean VBAC is unsafe or off the table for you. It's a conversation starter with your provider, not a verdict.
No. It's meant to support that conversation, not substitute for it. Your provider can factor in details this tool doesn't capture, like your specific c-section scar type, current pregnancy details, and hospital protocols.