In recent weeks a popular topic in the OB world is the update of the VBAC calculator to take out race! This was a big step in the right direction against some of the racial inequalities in the OB world. By having the race category in there it would calculate that someone of African American or Hispanic background had a significantly lower chance of having a VBAC compared to other races, which was not evidence-based in any way.
What is the VBAC calculator?
The VBAC calculator model that ACOG talks about in their 2019 Practice Bulletin calculates the percentage for birthing people with 1 prior low transverse c-section, with a singleton pregnancy in cephalic position. This model showed the highest predictability of VBAC in multiple countries to include the US, Europe, Asia, and Canada. This calculator was a tool that some providers used to determine the potential success rate of a vaginal birth after a cesarean birth.
But, this calculator included a race component that could really vary the results based on the ethnic background of the individual. For example, if you were African American, the calculator would calculator your success rate to be much lower than if you had put Caucasian as your ethnic background. You can see how this is an issue; the color of someone’s skin or their ethnic background should not be used as a predictor of a VBAC and is racially biased. This could cause providers to adjust their plan of care for someone based solely on the color of their skin.
So, what do they use to calculate a VBAC score now?
The calculator is basically the same as before minus the two race questions.
It’s based on:
age
height
pre-pregnancy weight
OB history (vaginal delivery- yes or no; if yes was it before or after c-section)
chronic hypertension
and was your prior c-section due to arrest of labor or descent?
Using these categories generates a percentage of how likely someone is to have a vaginal birth. So for example, if I was a 28year old who is 60inch tall and had a pre-pregnancy weight of 150, had no vaginal deliveries, no chronic blood pressure, and the reason for c-section was not due to arrest of labor it would give me a 56.8% chance of a VBAC. They would then base their recommendation to VBAC or have a repeat c-section based on this percentage.
They say a percentage of 60-70% is predictive of an outcome with fewer risks and less than 60% probability is associated with more risks associated with VBAC. There is no research that states the calculator improved patient outcomes.
There is some research that supports that the calculator predicts the outcome of VBAC or unplanned repeat c-section, but it’s also not super accurate. Some with low predictability of VBAC were still able to go on and have a VBAC, while others with high predictability still had a c-section. So the calculator should not be the ultimate decision-maker of whether or not someone should VBAC.
The percentage should be used to open the conversation between the patient and the provider, NOT make the decision for them. ACOG suggests using shared decision-making to weigh the risks and benefits and the birthing person individualized situation to make the decision of whether to VBAC or not. NOT using the percentage alone.