CLINICAL TOOL
VBAC Success & Rupture Risk Calculator
Clinical tool to estimate the probability of successful Vaginal Birth After Cesarean (VBAC) and the absolute risk of uterine rupture, assisting in shared decision-making.
About this page
This is a clinician-reviewed evidence brief, not an interactive calculator. It summarises the guideline logic our subspecialists apply when managing these cases every day. For a case-specific assessment, request a consultation or refer your patient.
Clinical Purpose
To provide personalized, evidence-based probabilities of successful Trial of Labor After Cesarean (TOLAC) versus repeat cesarean delivery, facilitating informed consent.
Inputs
- Maternal Age
- Body Mass Index (BMI)
- Race/Ethnicity
- Prior Vaginal Delivery (Before/After Cesarean)
- Indication for Prior Cesarean (e.g., Arrest of Dilation)
Formula & Guideline Source
MFMU Network VBAC Calculator (Grobman et al.), RCOG Green-top Guideline No. 45.
Limitations
Calculators are validated in specific populations. This tool estimates probabilities but cannot guarantee outcomes. Individual clinical factors (e.g., fetal weight, cervical status at term) significantly influence actual success.
FAQ
What is a 'good' probability for attempting VBAC?
While there is no universally agreed-upon threshold, many guidelines suggest a success probability of 60-70% or greater is associated with less maternal morbidity compared to an elective repeat cesarean delivery.
Does this tool calculate the risk of uterine rupture?
The tool incorporates baseline risks based on prior uterine incisions (e.g., ~0.5% for one prior low transverse incision). However, specific intrapartum factors (like induction of labor) can modify this risk.
References
- Grobman WA, et al. Development of a nomogram for prediction of vaginal birth after cesarean delivery. Obstet Gynecol. 2007.
- Royal College of Obstetricians and Gynaecologists. Birth After Previous Caesarean Birth. Green-top Guideline No. 45. 2015.