About the VBAC Calculator (Vaginal Birth After Cesarean Section)
This tool applies the Flamm-Geiger VBAC admission scoring system, a published intrapartum score (Flamm and Geiger, Obstetrics & Gynecology, 1997) used to estimate the likelihood of a successful vaginal birth after a prior cesarean delivery. It converts five clinical factors, available at the time a patient is admitted for labor, into a single point total from 0 to 10.
How the score is built
The total is the sum of five components:
- Maternal age: 2 points if under 40 years, 0 points at 40 or older.
- Prior vaginal delivery history: 0 points for none, 1 point for a vaginal delivery before the cesarean only, 2 points for a vaginal delivery after the cesarean only (a prior VBAC), and 4 points for a vaginal delivery both before and after the cesarean.
- Indication for the prior cesarean: 1 point if the indication was something other than an arrest disorder (for example breech presentation or fetal distress), 0 points if the indication was arrest of labor, failure to progress, or cephalopelvic disproportion.
- Cervical effacement at admission: 2 points for 75% or more, 1 point for 25-74%, 0 points below 25%.
- Cervical dilation at admission: 1 point for 4 cm or more, 0 points below 4 cm.
Adding the five parts together gives the Flamm-Geiger score, out of a maximum of 10 points.
Interpreting the result
In the original validation study, higher scores tracked with higher rates of successful VBAC: approximately 49% at 0-2 points, 60% at 3 points, 67% at 4 points, 77% at 5 points, 89% at 6 points, 93% at 7-8 points, and 99% at 9-10 points. These figures describe the study cohort as a group; they are not a guarantee for any individual pregnancy, and later obstetric history, fetal status, and how labor actually progresses all matter alongside the admission score.
When to consult a professional
This tool performs the standard Flamm-Geiger arithmetic for education and reference. It is not a diagnosis and does not direct a mode of delivery. The decision to attempt a trial of labor after cesarean, and how that labor is managed, should be made with an obstetric provider who can weigh this score alongside the full clinical picture.