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In a predominately Hispanic cohort receiving care through a community health center, we found that the updated MFMU Network calculator underestimated VBAC for those with no prior vaginal birth and/or an elevated BMI. Discouraging [labor after cesarean] based on a low probability score might have resulted in a marked decrease in the VBAC rate of this cohort by preventing both initial and subsequent VBAC. – Ledbetter et al. (2025)¹⁰ 

If you have had a prior cesarean, and your doctor is willing to consider a VBAC—which many aren’t—chances are they will offer to use a VBAC probability calculator to help guide your decision. Don’t accept. The short version of why not is that the calculator was developed by medical management practitioners. Practitioners with that mindset distrust labor, and the policies and practices that result from that bias will unnecessarily reduce VBAC rates below those that are achieved by practitioners who do trust it.

If my short version is good enough for you, feel free to scroll down to the “Takeaway” section, which will give you tips and tactics for how to maximize your probability of safe vaginal birth. If you want the long version, read on. The next section will summarize the study that was the source of the quote that opened this article and discuss the implications of its findings.

Why You Should Decline Using a VBAC Calculator

To understand the study, you first need to know more about the VBAC calculator that led to it.

To develop the calculator, obstetric researchers looked at a large population with previous cesareans and calculated the effects of various characteristics on the probability of VBAC (Grobman 2007).⁷ They then applied the results to individual profiles of members of the population to see whether the predicted VBAC rate correlated with the actual VBAC rate in those with that profile and found that it did. They published their results, and use of the calculator (and others like it) spread rapidly.

Subsequently, the same group set out to establish a cutoff point for recommending against or for labor after a cesarean (Grobman 2009).⁸ They determined, as they put it, that “maternal morbidity is not greater for those women who undergo [trial of labor] than those who undergo [elective repeat cesarean] if the chance of VBAC is at least 70%.” They also found that results were similar for babies regardless of probability of vaginal birth. (This latter finding is important because the reason given for denying VBAC is the risk to the baby, not the mother.)

At first glance, having a means of predicting your odds of VBAC and the threshold at which the risks tip in favor of labor seems like a good idea. However, the devil is in the details, which in this case is that the factors they included were maternal age, body mass index (BMI), race/ethnicity, prior vaginal delivery, prior VBAC, and prior cesarean for progress delay.

This brings us to the study I want to focus on here.

The impetus for the study was the removal in 2021 of race/ethnicity from the calculator as being racist—which, of course, it was, seeing as there is no plausible connection between darker skin pigmentation and decreased ability to birth vaginally—and that this factor was being used to discourage VBAC in women and birthing people of color (Ledbetter 2025).¹⁰ The investigators sought to determine whether removing race/ethnicity improved the accuracy of the updated VBAC calculator and to evaluate the potential effect of discouraging VBAC with predictions of less than 70 percent.

The study was conducted at a US community health center serving a Hispanic population in which midwives (75%) and family physicians (25%) provided care with obstetric collaboration in cases of complicated pregnancies. Spoiler alert: the health center’s cesarean rate was 15 percent compared with the US national cesarean rate of 32 percent, so already we know that something is different about care at this center compared with typical management.

Investigators reported on 507 labors after cesarean among 400 participants according to their observed versus predicted vaginal birth rate. Theoretically, removing race/ethnicity should have increased accuracy of VBAC probability in a population of color. The investigators found, however, that the observed VBAC rate in their population was 82 percent versus a predicted rate of 71 percent. Removing race/ethnicity from consideration had no benefit for people of color.

They didn’t stop there, though. They also reported on probability of VBAC in the presence of various characteristics according to the updated calculator compared with the observed VBAC rate in those with those same characteristics giving birth at the center.  (See Table.)

With the exception of prior VBAC, VBAC rates in the center’s population substantially exceeded the rate predicted by the calculator. Calculation revealed that scheduling a repeat cesarean with a predicted probability of VBAC less than 70 percent would have prevented 217 labors that ended in vaginal births. Applying the calculator and its 70 percent threshold would have increased the center’s repeat cesarean rate from 18 percent to 61 percent. In other words, advising against VBAC based on the calculator’s predictions would have unnecessarily exposed a large percentage of the community center’s population to the potential harms of cesarean surgery and the escalating risks of serial cesareans to them and their babies.

You now have proof of why you should decline use of a VBAC calculator. As you can see, care provider beliefs and their consequent policies have as much or more to do with your odds of VBAC than anything related to you. The VBAC calculator underpredicts VBAC because it reflects its developers’ bias in favor of repeat cesarean, and the effect of that bias is to reduce VBAC rates substantially below those achieved by practitioners for whom vaginal birth whenever safely possible is the goal.

Your Takeaway

Your takeaway from this article is that VBAC calculators are predicting VBAC rates based on the characteristics of the wrong people. Your task, then, is to do your own VBAC probability calculation. To begin with, you can’t just assume your doctor’s agreement to planning VBAC is sufficient. All too many agree at an early visit, but as the due date approaches, begin finding more and more qualifying hoops you must jump through or ratchet up pressure to agree to a cesarean. So, how can you determine if your doctor is truly VBAC friendly? Here are some questions that can help.

Tip: The first thing to find out is whether the doctors or midwives you’re seeing in pregnancy will be attending the birth. In some hospital systems, labors are managed on an on-call basis by physician employees of the hospital. If this is the case for you, you’ll need to ask questions about statistics and policies at the hospital where you are planning to have your baby.

• What percentage of your patients with a prior cesarean plan a VBAC? This number tells you whether this doctor truly encourages VBAC. This should be most of them since few circumstances contraindicate VBAC.
• What percentage of those who plan a VBAC have a vaginal birth? Considering that the practice will be a mix of those who have had a previous vaginal birth or VBAC, who are almost certain to do so again, and those who have not, who still have at least a 70 percent probability of having a VBAC, anything less than the mid 70 percents should count against them.
• Do you use a VBAC prediction calculator to advise me about candidacy for VBAC? As you saw, your doctor will be relying on a tool that will lowball your probability of VBAC.
• Under what circumstances would you recommend a repeat cesarean? These should be serious medical conditions or labor complications, not circumstantial reasons such as having a prior cesarean for slow progress, a baby estimated to be bigger than average, going past your due date, or failing to meet preset time limits for making progress in labor.
• Do all the others in your practice feel as you do about VBAC? If not, how can I ensure that I will be attended by someone who does? Most doctors and midwives are in group practices and rotate who is on call for births. It is entirely possible that some practice members don’t permit VBAC or hedge it with so many non-evidence-based restrictions that it amounts to the same thing.

Whether it’s because practices rotate call among their members, hospital employee physicians work shifts, or the doctor or midwife you counted on is out sick or on vacation, you probably won’t be able to ensure your birth attendant is a pro-VBAC practitioner.  Here are some ways you can maximize your probability of a safe VBAC:

• Hire a doula. Doulas will provide support for you, your partner, and other labor companions. They will be in your corner, counteracting any negative influences such as a disapproving nurse or unduly concerned doctor and helping you make informed decisions.
• Decline labor induction for non-medical reasons. Induction is a double hit for VBAC labors. It both increases the probability of the scar giving way—especially when an agent (prostaglandin E2, a.k.a., Cervidil, Dinoprostone, Minprostin) is used to ripen the cervix*—and decreases probability of vaginal birth (Goer 2012).⁶**

Tip: If induction is medically indicated, waiting for the cervix to be ready for labor brings VBAC rates up to those when labor starts on its own, and using an oxytocin regimen that “starts low and goes slow” will minimize the additional stress induced contractions impose on the uterine scar.

*Because of its strong association with scar rupture, misoprostol (Cytotec), another prostaglandin used for ripening an unfavorable cervix, is contraindicated for use in VBAC labors (ACOG 2019).¹

**In another example of bias among medical management practitioners, a study reported that the VBAC calculator may overestimate predicted probability of VBAC because it doesn’t factor in the effect of labor induction on decreasing it.

• Have patience if progress is slow. Studies show that VBAC labors progress more like first labors than labors after a prior vaginal birth (Chazotte 1990; Faranesh 2011; Harlass 1990).^{3, 5, 9}
• Avoid IV oxytocin to augment labor. As with induction, its use is associated with increased risk of the uterine scar giving way. Use physiologic strategies to get slow labors on track, such as staying mobile, and pushing in an upright position, such as squatting; however, if these don’t do the job, judicious use of IV oxytocin can avert a repeat cesarean.
• Consider alternative strategies to an epidural for labor pain. Epidurals offer complete pain relief, but they increase the need for IV oxytocin to augment labor. They can also cause episodes of slow fetal heart rate, which could lead to a misdiagnosis because a drop in fetal heart rate is the most common sign that the scar has given way (ACOG 2019).¹
• Decline a cesarean for prolonged labor if the only reason is because you have exceeded a preset time limit. If you don’t have a doctor you know is pro VBAC, cesareans for progress delay often amount to cesareans for the doctor’s failure to wait.
• Barring an emergency, take the time you need to consider your options so that you can make an informed choice. The BRAIN acronym can help you do this:

Benefits
Risks
Alternatives
Instinct/intuition
No or not now

You are entitled to know the benefits and risks of any proposed intervention and the benefits and risks of the alternatives, including doing nothing for now. Once you have digested that information, see what your instinct/intuition is telling you. Most importantly, you have the legal right to say, “no” or “not now.” If you do, it may be wise to discuss under what circumstances you would change—or consider changing—your mind.

Finally, while it is your right to decline as well as consent to any proposed treatment, the battle may cost you more of the staff’s good will than it is worth. Here are some compromises that may reduce the possibility of conflict by meeting hospital staff half way. It will be better to arrange for these ahead of time than raise them for the first time after admission in labor.

• Mandatory IV: Compromise on a saline lock. A saline lock is the business end of an IV, but you aren’t tethered to an IV pole. An IV can be started in seconds simply by connecting the IV bag’s tubing to the port on the saline lock.
• Oral intake is forbidden: Compromise on clear, calorie containing liquids. The concern is that should emergency general anesthesia be required—which it almost never is even when the scar is thought to have given way—it is possible to vomit when unconscious and inhale stomach contents (aspirate) into the lungs. This is a vanishingly rare possibility with proper anesthetic procedure (Goer 2012).⁶ We have no evidence that clear liquids cause any problems (Brady 2003),² and furthermore, aspirating undiluted stomach acid would pose the greater problem (Ludka 1993).¹¹
• Continuous fetal monitoring is required from time of hospital admission: Compromise on beginning continuous monitoring once you are experiencing strong, regular contractions. Continuous fetal monitoring in VBAC labors is the one difference from non VBAC labors for which a case can be made. The Society of Obstetricians and Gynaecologists of Canada’s (SOGC’s) VBAC guidelines, however, include a nuance: it recommends continuous fetal monitoring during “active labor” [emphasis mine] (Dy 2019).⁴ Provided you aren’t receiving IV oxytocin, likelihood of the scar giving way, already minimal, should be even more so in early labor when contractions are mild, and freedom to move around can help labor progress. You may also be able to get agreement to brief respite periods off the monitor to use the toilet or walk around a bit, which can help lift your spirits and feel “normal.”

Tip: Don’t let continuous fetal monitoring inhibit your mobility. Get creative: you can stand; slow dance with your partner; sit in a chair; squat, kneel upright, or assume hands and knees in bed while on the monitor. If your hospital has telemetry monitoring, which the SOGC recommends, you can stay mobile even while on the monitor (Dy 2019).⁴

References

1. ACOG. ACOG Practice Bulletin No. 205: Vaginal Birth After Cesarean Delivery. Obstet Gynecol 2019;133(2):e110-e27.
2. Brady M, Kinn S, Stuart P. Preoperative fasting for adults to prevent perioperative complications. Cochrane Database Syst Rev 2003(4):CD004423.
3. Chazotte C, Madden R, Cohen WR. Labor patterns in women with previous cesareans. Obstet Gynecol 1990;75(3 Pt 1):350-5.
4. Dy J, DeMeester S, Lipworth H, et al. No. 382-Trial of Labour After Caesarean. J Obstet Gynaecol Can 2019;41(7):992-1011.
5. Faranesh R, Salim R. Labor progress among women attempting a trial of labor after cesarean. Do they have their own rules? Acta Obstet Gynecol Scand 2011;90(12):1386-92.
6. Goer H. The case against elective repeat cesarean. In: Goer H., Romano A., eds. Optimal Care in Childbirth: The Case for a Physiologic Approach. Seattle, WA: Classic Day Publishing; 2012.
7. Grobman WA, Lai Y, Landon MB, et al. Development of a nomogram for prediction of vaginal birth after cesarean delivery. Obstet Gynecol 2007;109(4):806-12.
8. Grobman WA, Lai Y, Landon MB, et al. Can a prediction model for vaginal birth after cesarean also predict the probability of morbidity related to a trial of labor? Am J Obstet Gynecol 2009;200(1):56 e1-6.
9. Harlass FE, Duff P. The duration of labor in primiparas undergoing vaginal birth after cesarean delivery. Obstet Gynecol 1990;75(1):45-7.
10. Ledbetter A, Wandtke Herrmann T, Lupa K, et al. Observed Versus Predicted Vaginal Birth After Cesarean for Patients of a Community Health Center. J Midwifery Womens Health 2025;70(2):204-11.
11. Ludka LM, Roberts CC. Eating and drinking in labor. A literature review. J Nurse Midwifery 1993;38(4):199-207.