The decision to undergo a repeat c-section or try for a vaginal birth after cesarean can sometimes be a difficult one. One tool that you and your care provider may consider using is the VBAC Success Calculator. Originally published in 2007, the calculator uses data available at the first prenatal visit to come up with a likelihood that your VBAC will be successful.  

The VBAC calculator includes age, height and weight (pre-pregnancy), ethnicity, obstetrical history and the indication for the prior cesarean section. Each of these variables can be obtained at the first prenatal visit, giving women an early assessment of their chances. A different version of the calculator that is used at the time of hospital admission also adds information about gestational age, hypertensive disease of pregnancy, a recent cervical exam and whether your labor is being induced to come up with a more accurate prediction.

The calculator is based on data from over 7,000 trials of labor after cesarean at 19 different hospitals around the United States. Each of the women included had a singleton gestation in the vertex position, had one prior cesarean with a low-transverse uterine incision, and underwent a trial of labor after 36 6/7 weeks.  

The study that the calculator is based on found that women were more likely to have a successful VBAC if they were younger, had a lower pre-pregnancy BMI and were of white race. Also associated with a greater chance of VBAC is a nonrecurrent indication for the prior cesarean section (such as breech presentation or non-reassuring fetal heart tones) and a prior history of vaginal delivery. Older mothers, those with a higher BMI, and a maternal indication for the prior c-section such as failure to progress or failure to descend lower one’s chances of a successful VBAC.

The study does have several limitations. First, only women who have had only one prior cesarean section were included, making this tool less effective for those considering a VBA2C or higher. Second, it only looked at women who went into labor after 37 weeks. Women who go into spontaneous labor before 37 weeks or are induced for medical reasons should consult with their provider about whether a trial of labor should be attempted given the circumstances. Finally, it uses data from large academic medical centers, so women who give birth in a smaller hospital, birth center or home may find that their chances are much different depending on how supportive their provider is. 

It is important to recognize that even though the calculator has been validated numerous times, it should not be the only factor in your decision to attempt a VBAC. A woman with a 30% chance of a VBAC may still successfully do so, while a woman with an 80% chance may not. Though the calculator can be a useful tool in your decision to attempt a VBAC, finding a supportive provider and consulting with him or her about your past medical and surgical history, including the type of uterine incision you had, future family plans and your personal wishes is the most effective way to set yourself up for a safe and empowering birth experience.

Grobman WA, Lai Y, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU), "Development of a nomogram for prediction of vaginal birth after cesarean delivery," Obstetrics and Gynecology, volume 109, pages 806-12, 2007

To see your own chances, you can use the calculator online HERE