What does non-recurring cesarean indication mean for VBAC?

A non-recurring indication is a reason for the prior cesarean that is unlikely to happen again in a subsequent pregnancy, such as fetal malpresentation (breech, transverse lie), placenta previa, or maternal illness. A recurring indication, most commonly cephalopelvic disproportion (CPD) or failure to progress (dystocia), suggests that the pelvis may be too small for vaginal delivery again. Non-recurring indications add 1 point to the Flamm-Geiger score.

What is the overall VBAC success rate for women who attempt TOLAC?

According to ACOG (2010, reaffirmed 2020), approximately 60 to 80 percent of women who undergo a trial of labor after cesarean (TOLAC) achieve a successful vaginal delivery. Success rates vary by center, patient selection, and support for labor. Women with a prior vaginal delivery have the highest success rates (85 to 90%), while those with only prior cesareans have lower rates (50 to 65%).

Is VBAC safe for the baby and mother?

VBAC is associated with lower maternal morbidity compared to a repeat elective cesarean in most cases. The main risk is uterine rupture, which occurs in approximately 0.5 to 1% of TOLAC attempts (compared to 0.02% with elective repeat cesarean). If rupture occurs, it requires emergency surgery. ACOG recommends TOLAC only at facilities with immediate access to emergency cesarean and anesthesia. The calculator does not assess rupture risk, only VBAC success likelihood.

What does a VBAC score of 0 to 2 mean clinically?

A score of 0 to 2 corresponds to an estimated 49% VBAC success rate in the Flamm-Geiger model, meaning about half of women with these factors who attempt TOLAC will deliver vaginally. This is not a contraindication to TOLAC, but most clinicians use this as part of shared decision-making. Factors that commonly produce a low score include age 40 or older, no prior vaginal delivery, and a recurring CS indication such as dystocia.

How does a prior vaginal delivery affect VBAC success?

Prior vaginal delivery is the strongest predictor of VBAC success in the Flamm-Geiger model, contributing 4 points if the delivery occurred before the first cesarean, or 2 points if it occurred after a prior cesarean. A woman who delivered vaginally before her first cesarean has already demonstrated that her pelvis can accommodate a vaginal birth, which greatly increases the odds of a successful TOLAC.

What is a trial of labor after cesarean (TOLAC)?

TOLAC refers to allowing labor to occur in a woman who has had at least one prior cesarean delivery, with the intention of achieving vaginal birth (VBAC). TOLAC includes the labor attempt and all monitoring during labor. VBAC is the outcome when TOLAC succeeds in vaginal delivery. Not all TOLAC attempts result in VBAC; some end in repeat cesarean due to labor failure or other complications.

Is cervical effacement or dilation known before labor?

Cervical effacement and dilation at the time of hospital admission are assessed during a cervical exam when labor begins or when the patient presents to the hospital. These factors are not known before the onset of labor (unless a membrane sweep or pre-labor cervical check is done). Use Antenatal mode in this calculator to get a pre-labor estimate without cervical data; switch to Admission mode once you have cervical exam findings.

VBAC Calculator (Vaginal Birth After Cesarean)

Q: What is a good VBAC score using the Flamm-Geiger system?

A score of 8 to 10 is associated with approximately 93% VBAC success. A score of 6 is associated with 89% success, 5 with 77%, 4 with 67%, and 3 with 60%. Scores of 0 to 2 correspond to about 49% success. The highest contribution comes from a prior vaginal delivery before the first cesarean (4 points) and favorable cervical effacement (2 points).

Q: Can I have a VBAC after two prior cesareans?

The Flamm-Geiger score was derived from women with one prior cesarean. For women with two prior cesareans, TOLAC is considered riskier due to increased uterine rupture risk (estimated 1.5 to 2%). Many centers will offer TOLAC for two prior low-transverse uterine incisions after individual risk counseling. This calculator does not apply to the two-prior-CS scenario, and you should discuss this directly with a maternal-fetal medicine specialist.

Q: Does BMI affect VBAC success?

BMI is not part of the Flamm-Geiger score used in this calculator, but research shows that higher BMI is associated with lower VBAC success rates. A BMI above 30 is associated with success rates 10 to 20 percentage points lower than normal BMI. The Grobman 2007 MFMU antenatal model includes BMI as a continuous predictor. If your BMI is above 40, discuss this factor separately with your care team as it may significantly influence your individual TOLAC risk.

Score VBAC success likelihood using validated clinical factors from the Flamm-Geiger model. Enter delivery history and cervical findings for an instant estimate.

Maternal Age

Prior Vaginal Delivery History

Indication for Prior Cesarean

Cervical Effacement at Admission

Cervical Dilation at Admission

Maternal Age

Prior Vaginal Delivery History

Indication for Prior Cesarean

Cervical effacement and dilation are not yet known. The score range below shows the minimum (unfavorable cervix) to maximum (fully favorable cervix) possible at admission.

VBAC Score

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Estimated Success Rate

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Likelihood Category

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Score Range (Pre-labor)

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Estimated Success Range

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Likelihood Category

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🏥 What is a VBAC Calculator?

A VBAC calculator estimates the likelihood of a successful vaginal birth after cesarean (VBAC) based on validated clinical risk factors. Women who have had a prior cesarean section and wish to attempt vaginal delivery in a subsequent pregnancy undergo a trial of labor after cesarean (TOLAC). This calculator uses the Flamm-Geiger scoring system, published in Obstetrics and Gynecology (1997) and validated in a multicenter study of more than 5,000 women, to produce a numerical score from 0 to 10 and a corresponding estimated success rate from published outcome data.

The calculator serves several practical purposes: (1) Pre-labor counseling at prenatal appointments, where the Antenatal Estimate mode provides a score range before cervical assessment is possible; (2) Admission counseling at the hospital, where the Admission Score mode incorporates cervical effacement and dilation findings from the intake exam; (3) Shared decision-making between patients and obstetricians about whether to pursue TOLAC or schedule a repeat elective cesarean. According to ACOG Practice Bulletin 205 (2019), approximately 60 to 80 percent of women who attempt TOLAC will achieve a successful VBAC.

A common misconception is that a prior cesarean automatically prevents vaginal delivery. In practice, the majority of women with one prior low-transverse uterine incision who attempt TOLAC succeed. The main concern is uterine rupture, which occurs in approximately 0.5 to 1 percent of TOLAC attempts. This risk must be weighed against the risks of a repeat elective cesarean, including increased surgical morbidity with each subsequent operation, longer recovery, and risks for future pregnancies (placenta accreta spectrum). The calculator addresses only the probability of VBAC success, not the relative risk of rupture, which requires an individualized conversation with your care team.

The Flamm-Geiger model includes five clinical factors: maternal age, prior vaginal delivery history, indication for the prior cesarean, cervical effacement at admission, and cervical dilation at admission. Of these, prior vaginal delivery before the first cesarean is the strongest predictor, contributing 4 of a possible 10 points. Cervical effacement at or above 75 percent contributes 2 points, and maternal age below 40 contributes 2 more. Together these three factors can account for 8 of the maximum 10 points.

📐 Formula

VBAC Score (0–10) = Age pts + Vaginal History pts + Indication pt + Effacement pts + Dilation pt

Age: under 40 years = 2 pts; 40 or older = 0 pts

Vaginal delivery history: any vaginal delivery before first CS = 4 pts; vaginal delivery only after CS = 2 pts; none = 0 pts

CS indication: non-recurring (malpresentation, preeclampsia, placenta previa) = 1 pt; recurring (dystocia, CPD, failure to progress) or unknown = 0 pts

Cervical effacement at admission: 75% or more = 2 pts; less than 75% = 0 pts

Cervical dilation at admission: 4 cm or more = 1 pt; less than 4 cm = 0 pts

Maximum possible score: 2 + 4 + 1 + 2 + 1 = 10 points

Score-to-success-rate mapping (Flamm and Geiger, 1997):

Score 0 to 2 = approximately 49% success

Score 3 = approximately 60% success

Score 4 = approximately 67% success

Score 5 = approximately 77% success

Score 6 = approximately 89% success

Score 7 to 10 = approximately 93% success

The Flamm-Geiger scoring system was developed from logistic regression analysis of 5,022 women undergoing TOLAC at 17 medical centers. It predicts VBAC success with an area under the ROC curve of approximately 0.71, which is considered a good discriminator for a 5-factor clinical model. The score does not account for induction of labor, gestational age, fetal weight estimate, or type of uterine incision, all of which can further modify individual risk. It should be used alongside, not instead of, a full obstetric assessment.

📖 How to Use This Calculator

Steps

Choose calculation mode - Select Admission Score if you have cervical exam findings from a hospital admission. Select Antenatal Estimate during a prenatal visit when cervical data is not yet available.

Enter maternal age and vaginal delivery history - Select whether the mother is under 40, and choose the type of prior vaginal delivery: before the first cesarean (strongest predictor), only after a prior cesarean, or no prior vaginal delivery at all.

Select the indication for the prior cesarean - Non-recurring indications (malpresentation, preeclampsia, placenta previa) add 1 point because they are unlikely to recur. Recurring indications (dystocia, CPD) add 0 points because they may recur.

Enter cervical exam findings in Admission mode - Select whether effacement is at least 75% and whether dilation is at least 4 cm. These two factors together can add up to 3 additional points.

Click Calculate for your VBAC score - The calculator shows your total Flamm-Geiger score, the estimated success rate from published outcome data, and a likelihood category. Use this alongside your obstetrician's clinical assessment.

💡 Example Calculations

Example 1 - Favorable Candidate (Score 10)

Age 32, vaginal delivery before CS, non-recurring CS, effacement 90%, dilation 5 cm

Age under 40: +2 points. Prior vaginal delivery before first CS: +4 points. Non-recurring CS indication (prior CS for breech presentation): +1 point.

Cervical effacement 90% (at or above 75%): +2 points. Cervical dilation 5 cm (at or above 4 cm): +1 point.

Total score = 2 + 4 + 1 + 2 + 1 = 10 out of 10. This corresponds to an estimated 93% VBAC success rate per the Flamm-Geiger model. This patient is a highly favorable TOLAC candidate.

Score = 10 / 10 | Estimated success = 93%

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Example 2 - Less Favorable Candidate (Score 2)

Age 42, no prior vaginal delivery, CS for dystocia, effacement 40%, dilation 2 cm

Age 42 (not under 40): 0 points. No prior vaginal delivery: 0 points. Prior CS for dystocia (recurring indication): 0 points.

Cervical effacement 40% (less than 75%): 0 points. Cervical dilation 2 cm (less than 4 cm): 0 points.

Total score = 0 out of 10. This corresponds to an estimated 49% success rate. A score of 0 to 2 means roughly half of women with these factors who attempt TOLAC will succeed. This is a lower-likelihood scenario that warrants careful individualized counseling.

Score = 0 / 10 | Estimated success = 49%

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Example 3 - Pre-labor Antenatal Estimate

Age 35, vaginal delivery after CS only, non-recurring CS indication (prenatal visit)

Age under 40: +2 points. Prior vaginal delivery only after a CS: +2 points. Non-recurring CS indication (prior CS for malpresentation): +1 point. Pre-labor base score = 5 out of 10.

Cervical factors are not yet known. With unfavorable cervix (effacement under 75%, dilation under 4 cm), the score remains at 5 (estimated 77% success). With a fully favorable cervix at admission (effacement 75%+, dilation 4 cm+), the score reaches 5 + 3 = 8 (estimated 93% success).

Pre-labor score range = 5 to 8 out of 10. Estimated success range = 77% to 93%. This patient is a moderate-to-high likelihood TOLAC candidate, with final odds depending on cervical status at admission.

Pre-labor score range = 5 to 8 / 10 | Estimated success = 77% to 93%

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❓ Frequently Asked Questions

What is a good VBAC score using the Flamm-Geiger system?+

A score of 8 to 10 corresponds to approximately 93% VBAC success, and a score of 6 corresponds to 89%. Many clinicians consider a score of 5 or above (77% success) to be a strong TOLAC candidacy indicator. Scores of 0 to 2 correspond to about 49% success, which is still a coin-flip outcome but warrants careful shared decision-making. There is no universally agreed cutoff below which TOLAC is contraindicated by score alone.

What does a non-recurring cesarean indication mean for VBAC?+

A non-recurring indication is a reason for the prior CS that will not be present in the current pregnancy, such as fetal malpresentation (breech, transverse lie), placenta previa, or a maternal condition like severe preeclampsia. These indications score 1 additional point because they do not predict that vaginal delivery will fail again. A recurring indication, most commonly failure to progress (dystocia) or suspected cephalopelvic disproportion (CPD), scores 0 points because the same mechanical barrier may still exist.

What is the overall VBAC success rate for women attempting TOLAC?+

ACOG Practice Bulletin 205 states that approximately 60 to 80 percent of women attempting TOLAC achieve a successful VBAC. Women with a prior vaginal delivery have rates of 85 to 90 percent. Women with only a prior cesarean and no vaginal delivery history have rates of 50 to 65 percent. Success rates also vary by induction status: spontaneous labor has higher success rates than induced labor for TOLAC.

Is VBAC safe for the baby and the mother?+

VBAC, when successful, carries lower maternal morbidity than a repeat elective cesarean, including less blood loss, shorter hospital stay, and faster recovery. The main risk of TOLAC is uterine rupture, which occurs in 0.5 to 1 percent of attempts at a low-transverse scar. Rupture requires emergency cesarean and can threaten fetal and maternal life. ACOG recommends that TOLAC occur only at centers with immediate cesarean capability. The risk must be weighed individually against the risks of repeat cesarean, which increase with each subsequent operation.

Can I have a VBAC after two prior cesareans?+

The Flamm-Geiger score was validated only in women with one prior cesarean. For women with two prior low-transverse incisions, TOLAC is possible but carries a higher uterine rupture risk (approximately 1.5 to 2 percent). Some high-volume centers offer TOLAC for two prior cesareans after careful individualized counseling. This calculator does not apply to the two-prior-cesarean scenario; discuss your specific situation with a maternal-fetal medicine (MFM) specialist.

How does prior vaginal delivery affect VBAC success the most?+

Prior vaginal delivery before the first cesarean is the single strongest predictor in the Flamm-Geiger model, contributing 4 of the maximum 10 points. It demonstrates that the pelvis has successfully accommodated a vaginally delivered fetus. A prior vaginal delivery only after a cesarean contributes 2 points, which still reflects demonstrated pelvic capacity even though the cesarean came first. No prior vaginal delivery scores 0 points and often reflects nulliparous women whose first delivery ended in a cesarean.

What is the difference between TOLAC and VBAC?+

TOLAC (trial of labor after cesarean) is the process: allowing labor to proceed in a woman who has had at least one prior cesarean. VBAC (vaginal birth after cesarean) is the outcome: a successful vaginal delivery after TOLAC. Not all TOLAC attempts result in VBAC. Some TOLAC attempts end in an unplanned repeat cesarean due to labor failure, non-reassuring fetal status, or other complications. This calculator estimates the probability of VBAC, meaning the likelihood that TOLAC will end in vaginal delivery.

Does BMI affect VBAC success rate?+

BMI is not a factor in the Flamm-Geiger score used here, but research consistently shows that higher BMI reduces VBAC success. A BMI above 30 is associated with VBAC success rates 10 to 20 percentage points lower than for normal BMI. The Grobman 2007 MFMU antenatal model, a separate validated tool, includes BMI as a continuous variable. If your BMI is above 40, discuss this directly with your care team as it substantially modifies your individual TOLAC risk assessment.

Are cervical effacement and dilation known before labor starts?+

Typically, no. Cervical effacement and dilation are assessed by a provider doing a vaginal exam, usually at hospital admission when labor has begun or membranes have ruptured. During prenatal visits, some providers perform cervical checks in the third trimester, but these findings can change rapidly as labor approaches. Use the Antenatal Estimate mode in this calculator during prenatal visits, and switch to Admission Score mode once you have an actual cervical exam result at the hospital.

What uterine incision type is required for VBAC eligibility?+

TOLAC candidacy per ACOG requires a prior low-transverse uterine incision (the horizontal cut made in the lower uterine segment). A prior classical (vertical) incision carries a uterine rupture risk of 4 to 9 percent and is generally a contraindication to TOLAC. A prior low-vertical incision or T-incision also carries higher rupture risk than a low-transverse scar. This calculator assumes a low-transverse prior incision. If you have had any other type of incision, consult your obstetrician before using this score.

Does induction of labor affect VBAC success or safety?+

Yes. Induction of labor for TOLAC is associated with lower VBAC success rates compared to spontaneous labor, and with a modestly higher uterine rupture risk. ACOG advises against using prostaglandins (misoprostol, PGE2) for cervical ripening in TOLAC due to elevated rupture risk. Oxytocin induction is generally considered acceptable but should be monitored carefully. These factors are not included in the Flamm-Geiger score; discuss induction plans with your care team as a separate consideration.

🔗 Related Calculators

📌 Quick Tips

💡The single strongest predictor of VBAC success is a prior vaginal delivery before the first cesarean. Women with this history have approximately 4 times the score contribution of any other single factor.

💡Use Antenatal mode during prenatal visits to get a pre-labor estimate before a cervical exam is possible. Switch to Admission mode once admitted to hospital and a cervical exam has been performed.

💡A score of 0 to 2 does not mean VBAC is impossible, just that statistically fewer attempts succeed. Many clinicians and patients still choose trial of labor (TOLAC) at this score after shared decision-making.

💡The Flamm-Geiger score was validated in a multicenter study of over 5,000 women published in Obstetrics and Gynecology (1997). It remains one of the most cited tools for VBAC counseling in obstetric practice.

💡This calculator is an educational tool for informed decision-making. Always discuss your individual VBAC plan with a qualified obstetrician who knows your full medical and obstetric history.