• Antenatal counseling for patients with one prior low-transverse cesarean section (LTCS) contemplating Trial of Labor After Cesarean (TOLAC).
• Standardizing shared decision-making regarding mode of delivery at 37 0/7 to 41 6/7 weeks gestation.
• Informing patients of their individualized probability of successful vaginal birth versus repeat cesarean.

• Single prior low-transverse uterine incision.
• Singleton pregnancy.
• Cephalic presentation.
• Term gestation (≥37 weeks).

The model utilizes a logistic regression equation. Prior vaginal delivery is the strongest positive predictor of success, reflecting a "proven" pelvis. Conversely, a prior CS performed for an arrest disorder (failure to progress or fail to descend) suggests a recurring mechanical or physiological barrier, reducing the likelihood of success in subsequent trials.

• Prior VBAC is the single best predictor of future success (rates often >90%).
• The calculator is most accurate for patients who enter labor spontaneously.
• A success probability of >60-70% is generally considered "favorable" for a trial of labor.

• Does not account for induction of labor — induction reduces success rates by ~10-15% compared to spontaneous labor.
• Inter-pregnancy interval < 18 months significantly increases risk of uterine rupture.
• Estimated fetal weight (EFW) > 4000g decreases probability of success but is not a variable in this specific model.

• Counsel patient on the high likelihood of successful vaginal delivery.
• Discuss the benefit-risk ratio: Lower maternal morbidity compared to repeat CS if successful.
• Document shared decision-making for TOLAC.
• Ensure facility allows for "immediate" emergency CS should rupture occur.

• Counsel patient that while VBAC is still possible, the risk of "failed" TOLAC is higher.
• Explain that a failed TOLAC (maternal morbidity) is riskier than a scheduled repeat CS.
• Consider Elective Repeat Cesarean Delivery (ERCD) if the patient prioritizes avoiding labor or failed trial.

The Maternal-Fetal Medicine Units (MFMU) Network was established by the NICHD to conduct large-scale clinical trials in obstetrics. This calculator is the result of massive multi-center data collection aimed at reducing the rising primary cesarean rate in the US.

A leading figure in MFM and obstetric health services research. Dr. Grobman championed the removal of race from clinical algorithms to ensure that evidence-based tools do not inadvertently reinforce health inequities.