Thursday, August 31, 2017

Lower Surgical Threshold, Less Patience in Labor for "Obese" Women


Here is yet another study (Ellekjear 2017) showing that labor is often managed differently in "obese" women, with a lower surgical threshold being the most marked finding. The authors concluded:
Caesarean deliveries are undertaken earlier in obese women compared to normal weight women following the onset of active labour, shortening the total duration of active labour.
Research generally shows women of size probably need more time in labor in general, especially in the early stages, but once their labors get going, they usually go well. However, many care providers opt to terminate labor earlier and move quickly to a cesarean. They are understandably concerned about the risks of doing an emergent cesarean on a larger body, but they are usually giving up far too soon and causing an epidemic of "failure to wait" cesareans in women of size. .

There was an infamous Vaginal Birth After Cesarean (VBAC) and obesity study in 2001 that demonstrated this quite strongly. 30 women over 300 lbs. were "allowed" to labor for a VBAC, but only 13% of those who tried for a VBAC ended up with one. As a result, this was widely publicized as a reason not to "let" high-BMI women try for a VBAC and cited by doctors as a reason to deny fat women the opportunity to VBAC.

However, what the full text of the study actually reveals is that the majority of these women were induced, which is known to increase the chances of cesarean and lower the chances of VBAC. Interestingly, the only women who got a VBAC in this study were the ones who were not induced.

Most tellingly, those who had cesareans had their labors stopped at an average of 4.5 cm of dilation. 4.5 cm barely qualifies for the old definition of active labor, and certainly doesn't fit with the new recommended definition of active labor (6 cm)! In other words, these high BMI women were not given an adequate chance to labor.

High induction rates and a lack of patience in labor are the main factors that drive the high cesarean rate in obese women. 

Studies have shown that about half of high BMI women in general are induced, typically increasing cesarean rates. However, when allowed to go into spontaneous labor, cesarean rates are more equalized among BMI groups.

One earlier study found that high BMI women tended to take longer to progress in labor, especially between 4 and 7 cm of dilation. They urged far more patience in the labors of heavier patients.

Similarly, a 2016 study found that 57% of labors in high BMI first-time mothers were stopped before 6 cm of dilation; those mothers ended with cesareans. Failure to Wait is a major problem when doctors attend women of size.

More spontaneous labor and more time during labor would probably have yielded far better VBAC rates in that 2001 VBAC study. It should be pointed out that a look at some later studies showed VBAC rates around 50-70% in obese women, which could almost certainly be increased even more since they also reflect very high induction rates and the old active labor definition. Indeed, research from England shows that the majority of even very high BMI women can have a vaginal birth with different management.

The bottom line is that multiple studies have found that the labors of high BMI women are managed differently than the labors of average-sized women. 

In particular, too many inductions are being done, the surgical threshold is very low, and more patience is needed during labor. This represents an area that is ripe for change and offers hope for lowering the far-too-high cesarean rate in obese women. 

As the authors of a Canadian study concluded about the management of high BMI women:
Because of the potential morbidities associated with Caesarean section, we must modify our management approaches to allow equal opportunity for a vaginal birth for all women.

Reference

BMC Pregnancy Childbirth. 2017 Jul 12;17(1):222. doi: 10.1186/s12884-017-1413-6. Maternal obesity and its effect on labour duration in nulliparous women: a retrospective observational cohort study. Ellekjaer KL, Bergholt T, L√łkkegaard E. PMID: 28701155
...METHODS: Retrospective observational cohort study of 1885 nulliparous women with a single cephalic presentation from 37 0/7 to 42 6/7 weeks of completed gestation and spontaneous or induced labour at Nordsj√¶llands Hospital, University of Copenhagen, Denmark, in 2011 and 2012. Total duration of labour and the first and second stages of labour were compared between early-pregnancy normal-weight (BMI <25 kg/m2), overweight (BMI 25-29.9 kg/m2), and obese (BMI ≥30 kg/m2) women. Proportional hazards and multiple logistic regression models were applied. RESULTS: Early pregnancy BMI classified 1246 (66.1%) women as normal weight, 350 (18.6%) as overweight and 203 (10.8%) as obese. No difference in the duration of total or first stage of active labour was found for overweight (adjusted HR = 1.01, 95% CI 0.88-1.16) or obese (adjusted HR = 1.07, 95% CI 0.90-1.28) compared to normal weight women. Median active labour duration was 5.83 h for normal weight, 6.08 h for overweight and 5.90 h for obese women. The risk of caesarean delivery increased significantly for overweight and obese compared to normal weight women (odds ratios (OR) 1.62; 95%CI 1.18-2.22 and 1.76; 95%CI 1.20-2.58, respectively). Caesarean deliveries were performed earlier in labour in obese than normal-weight women (HR = 1.80, 95%CI 1.28-2.54). CONCLUSION: BMI had no significant effect on total duration of active labour. Risk of caesarean delivery increased with increasing BMI. Caesarean deliveries are undertaken earlier in obese women compared to normal weight women following the onset of active labour, shortening the total duration of active labour.

Sunday, August 20, 2017

Researchers' Goof: Transverse CS Incisions ARE Better in High BMI Women!


EXTRA, EXTRA! 

Researchers messed up the conclusion of earlier cesarean incision study! 

Transverse (side-to-side) incisions really are better after all for high BMI women! 

Vindication! 

Background

For many years OBs were taught that a vertical incision was needed for very "obese" women because the area under a belly flap ("panniculus", sometimes referred to as a "pannus") was hot and moist and therefore prone to infection ─ in other words, an area just waiting to cause wound complications. One OB wrote in 2006:
In general, there is a lot to be said for an incision not buried under the pannus of fat, so that fresh air can help keep the wound dry.
As a result, many OBs were taught that when they did cesareans on high BMI women, vertical (up-down) incisions should be used instead of low transverse (side-to-side, either Pfannenstiel or Joel-Cohen) incisions in order to lower the risk for infection, separations, and other wound complications.

WRONG! Example of incorrect teaching illustration
about vertical incisions and obesity
They meant well, but they were operating from flawed assumptions and outdated teaching. In other words, they hadn't actually studied whether or not vertical was better in high-BMI women, they just assumed it was, based on their biases about fat bodies. As the authors of Alanis 2010 state:
Our results...contradict classic teaching by veteran surgeons and obstetrical texts. It has been written that transverse abdominal incisions made under the pannicular fold exist in “a warm, moist, anaerobic environment associated with impaired bacteriostasis . . .[that] promotes the proliferation of numerous microorganisms, producing a veritable bacteriologic cesspool.” However, we are unable to locate any evidence to support this popular conclusion....
A "veritable bacteriologic cesspool"? What a terrible and disrespectful way for those obstetric texts to describe it. While deep skin folds can sometimes predispose to skin yeast and infections, it doesn't always and surgical incisions should not be based on conditions assumed to exist. Rather, care providers should be aware of the possibility and make decisions based on actual evidence of problems rather than an assumption of pathology.

Vertical Incisions Do Not Improve Outcomes


As noted, cesarean incision choice for very heavy women was usually based on traditional teachings and biased assumptions. When someone actually took the time to research these hypotheses, however, it was found that vertical incisions were no better, and in some studies were actually far more risky.

Let's do a quick review of the medical literature on this topic.

Vertical is More Risky

The Alanis 2010 study discussed above studied women with a BMI over 50. They found better outcomes with transverse incisions:
Vertical abdominal incisions were associated with increased operative time, blood loss, and vertical hysterotomy...Our results also support the use of Pfannenstiel incisions in obese patients with a large panniculus.
D'heureux-Jones 2001 also found that vertical incisions were associated with greater blood loss and poorer outcomes. They recommended a Pfannenstiel incision too.

In some studies the findings were more dramatic. In Wall 2003, vertical incisions presented 12x the risk for wound complications compared to transverse incisions. TWELVE TIMES the risk. That's a tremendous difference.

Thornburg 2012 found that the majority of wound complications (WC) were found in the vertical incision group (45.7% rate in vertical incisions, vs. 11.6% in transverse incisions). That's a very significant difference. They concluded:
In morbidly obese women both infectious and separation type WC are more common in vertical than low transverse incisions; therefore transverse should be preferred.
Vertical is No Improvement

Critics would point out that a number of studies did not find a statistically significant difference between vertical vs. low transverse incisions (Sutton 2016, Vermillion 2000McLean 2012, Houston and Raynor 2000Brocato 2013, and Bell 2011). Many researchers cite these studies to argue that there is no difference between incisions and the choice should be completely left to the surgeon's preference.

However, if they read the full text of these studies, the data usually showed a very clear trend towards more complications with vertical incisions. For example, 5 of the 6 above-cited studies found nearly double or more the rate of problems in the vertical incision group, yet the difference did not rise to statistical significance:
  • Bell 2011 found wound complications in 14.6% of the vertical incision group vs. 7.6% in the low transverse group
  • Vermillion 2000 found a 23% wound infection rate in the vertical group vs. a 6% rate in the low transverse group
  • McLean 2012 found a 20% rate of wound separation in the vertical group vs. a 10% rate in the low transverse group
  • Sutton 2016 found a 26.3% rate of wound complications in the vertical group vs. 14.8% in the low transverse group 
  • Brocato 2013 found 2.7x the risk for wound complications in the vertical group
The problem here is that the number of patients in the vertical incision groups in these studies was extremely small and that is what is confusing the outcome. Bell 2011 had only 41 patients with vertical incisions; Brocato 2013 had only 45; Sutton 2016 had only 57; McLean 2012 had only 25; and Houston and Raynor 2000 had only 15 patients in their vertical comparison groups. Basically, the studies showing no significant difference had too few vertical incisions to be rigorously compared. 

The fact that the differences didn't rise to statistical significance doesn't mean that vertical incisions were just as safe; it just means that these studies were simply underpowered to show statistical significance between the groups. 

Summary

Larger studies do need to be done, but the majority of the evidence we have so far suggests that vertical incisions perform no better and often perform worse in obese women. Low transverse incisions are usually associated with better outcomes. 

Bottom line, vertical incisions are associated with increased rates of wound complications, blood loss, and infections in obese women, even very obese women, as we have written about extensively before. In addition, vertical incisions are far more scarring and challenging to a woman's self-esteem and should ideally be avoided on that basis alone. It's also worth noting that although the best incision for each woman's unique anatomy and situation must be judged on an individual basis, low transverse incisions have been used successfully even in women of 400-500 pounds without poor outcomes.

Vertical Skin = Vertical Uterine Incisions

Image from swcare.net

Another problem is that several of these studies (Bell 2011, Alanis 2010, Sutton 2016) have also shown that when vertical skin incisions are done, they result in a higher rate of vertical uterine incisions (hysterotomies). Bell 2011 found that nearly 2/3 of all vertical skin incisions in obese women resulted in a vertical uterine incision as well.

A vertical uterine incision results in a riskier surgery, with more blood loss, a more difficult recovery, and a higher rate of uterine rupture in future pregnancies. In most OB practices, it limits a woman's future delivery choices to automatic repeat cesareans, which may have tremendous long-term health implications for the mother due to increased placental abnormalities and intraoperative injuries. The Alanis 2010 authors noted:
Vertical abdominal incisions were associated with vertical hysterotomy in our study, usually a result of inadequate access to the lower uterine segment. When the incision extends into the contractile portion of the uterus, a vertical hysterotomy has a profound impact on future pregnancy. Therefore, it is important to incorporate practices, like transverse abdominal incisions, that facilitate low uterine incisions.
Doing a vertical incision routinely and without pressing need in high BMI women subjects them to more risk and potentially limits their future reproductive choices. As a result, one reviewer concluded that in obese women:
Low transverse skin incisions and transverse uterine incisions are definitely superior and must be the first option.
In recent years, more and more OBs began to use low transverse incisions in women of size. In fact, today the vast majority of high BMI women ─ even very high BMI women ─ who have cesareans have low transverse incisions. This is encouraging progress.

Still, many OBs cling to their teaching and use a vertical incision at a higher rate for obese women, especially "morbidly obese" and "super obese" women.

2016 survey of OBs revealed that while 84% preferred a transverse incision for obese women, 16% still preferred other incisions (usually vertical).

McLean 2012 found that 11% of high-BMI women were still being subjected to the riskier vertical incisions; Marrs 2014 (a very large, multi-region, multi-center study; see below) found that vertical incisions were used in a whopping 19% of high BMI women.

Between these documents, that's a vertical incision in about 1 out of every 5-10 cesareans done in obese women. So while progress has been made, vertical incisions are still distressingly common, and they are still putting the well-being of women of size at risk.

But What About That 2014 Study?



Some doctors have pointed to the Marrs 2014 study to justify continuing with vertical incisions. This was the one study that seemed to disprove the idea that transverse was better. (See the first abstract below, full text can be found here.)

This was a secondary analysis of the MFMU registry, which examined data from cesareans in 19 different regional hospitals. This analysis looked at incision complications after cesarean in women with a BMI of 40 or more. Since it was the largest study of its kind in obese women (597 vertical incisions, 2603 transverse incisions), its conclusions were assumed to be far more powerful and definitive.

In the study, wound complications were found in 1.7% of women with transverse incisions vs. 4.2% of women with vertical incisions. In other words, more than double the rate of problems were found with vertical incisions. Simple conclusion to be drawn, right? Not quite.

In its univariate (one variable) analysis, transverse was shown to be the safer incision. But in its multivariate (multiple variable) analysis, the opposite was found ─ vertical seemed better. This conclusion was trumpeted far and wide because now there was research ammo to keep justifying the use of vertical incisions in high-BMI women.

However, a re-analysis of the data shows that their conclusion was wrong and transverse was better after all. Turns out they used the wrong figures in their multivariate analysis and so got the wrong conclusion. Instead of vertical being the better incision, it was actually transverse that had the best outcomes. The authors issued a retraction in July of 2017 and stated:
The original publication reported that univariate analysis showed that a vertical skin incision in obese women undergoing Cesarean delivery was associated with a higher odds ratio for wound complications than a transverse skin incision. Multivariable analyses showed a reversal of the association (i.e. the odds of wound complications were lower in women with a vertical skin incision). However, there was an error in the way the variable was entered in the logistic analysis. Re-analysis with the correct coding of the variable indicates that a transverse skin incision is associated with decreased odds of wound complication compared to a vertical skin incision.
Well, bravo that they finally published a retraction to the previous study and a corrected abstract...3 years after the fact. (I have published the abstracts to both below for comparison.)

At least they actually printed a retraction and admitted their error. Usually these are just glossed over. But I'm irritated because the damage has been done. How many OBs have gotten the wrong impression and won't see the retraction? How many young doctors have been erroneously taught that vertical incisions were superior for high BMI women?

When you search online, the original manuscript with its erroneous conclusions still pops up without any corrections, and is still being cited by some doctors as evidence that a vertical incision is just as good or better.

How many high-BMI women have had the more dangerous vertical incision in the meantime and how many will continue being subjected to it because of the error in that original study? How many medical schools and textbooks will continue teaching that vertical incisions are better?

Grrrrrrrr. Mistakes happen, but this is a mistake with long-lasting implications for larger women. I can't believe they were sloppy enough to make this mistake in the first place and then not discover it for three years. I also question whether they are doing enough to reach out to correct the mistaken teaching and care practices that are in place because of this egregious error. If it's not addressed aggressively, incorrect teachings and practices will remain in place, and that could have a lot of negative health implications for women of size.

Conclusion

Low transverse cesarean scar in a high BMI woman;
these are usually minimally noticeable after a few years


A vertical skin incision on a high BMI woman has far more noticeable
scarring and potential impact on her self-esteem

The cesarean rate in obese women is unconscionably high. Some cesareans are needed of course, but many cesareans in high BMI women are planned pre-labor cesareans, and many labor cesareans could probably be avoided with more patience, fewer inductions, a more lenient surgical threshold, and different management in labor.

But the fact of the matter is that around half or more of all obese mothers in many areas of the U.S. are being subjected to cesareans. The rate of wound complications increases with BMI in a dose-respondent manner, so the question of how to lower complications in obese women is extremely pressing.

Proper choice of cesarean incision is one key way to reduce complications in obese women. Thankfully, most OBs recognize that a low transverse is the best incision in high BMI women, and use it most of the time.

However, some OBs continue to insist that vertical is better, especially as BMI increases. One 2014 study found only a 2% rate of vertical incisions in women with BMIs between 30 and 40, but this increased to more than 15% in women with a BMI over 50. The fact that the Marrs MFMU study found that vertical incisions were used in 19% (nearly 1 in 5 cesareans of obese women) in women with a BMI over 40 is quite alarming. These high rates are risking the health and well-being of women of size.

Furthermore, OBs have even been known to use a vertical incision to discourage their "morbidly obese" patients from having more children. This is appalling example of weight stigma. Here is one woman's story:
When she came in to discuss my surgery, the OB sat down and asked me if I wanted my tubes tied while she was in there. I was shocked and told her no, that this was my first child, and I didn't want to make decisions like that at the moment. And she countered with a speech that boiled down to 'You are too fat to have any more children, you shouldn't even be having this one, and if I had anything to do with it, you wouldn't be.'...[Afterwards] the hateful OB informed me that the kind of incision that they made in my uterus will make it incredibly dangerous for me to attempt another pregnancy...a subsequent pregnancy could cause the uterus to rupture and I would die horribly from a hemorrhage.
Granted, there are sometimes circumstances which compel the use of a vertical incision. An extremely large belly makes it harder to locate anatomical landmarks; sometimes the panniculus is so large it is impossible to place an incision beneath it; sometimes there is an active skin infection present in the folds; sometimes other factors like fetal or placental position make a different incision safer. In those situations, there are other incision options, including a vertical or a higher transverse (Joel-Cohen) incision. However, this mother had none of these considerations. The incision seems to have been chosen purely to punish the mother and to strongly discourage further children despite her refusal of sterilization.

Whatever the reasons, there is no justification for such a high rate of vertical incisions still being used in heavy women. Medical schools and educational materials need to stop teaching that a vertical incision is the incision of choice for high BMI women.

Research CLEARLY shows that a vertical incision performs no better than a transverse one in obese women and in most research, is actually associated with worse outcomes. NO study now shows a better outcome with vertical incisions. 

The bottom line is that incision choice for each woman of size must be evaluated on its individual circumstances, but a low transverse incision should be the default choice in nearly all high BMI women. As one OB said in a conference presentation to colleagues:
The bottom line is that vertical incisions should not be used in obese patients...Vertical incisions are being used less and less in these patients, but just don't do it.

References

Original Article

Am J Obstet Gynecol. 2014 Apr;210(4):319. doi: 10.1016/j.ajog.2014.01.018. Epub 2014 Feb 20. The relationship between primary cesarean delivery skin incision type and wound complications in women with morbid obesity. Marrs CC, Moussa HN, Sibai BM, Blackwell SC. Full text here.
OBJECTIVE: We sought to evaluate the relationship between skin incision, transverse or vertical, and the development of wound complications in women with morbid obesity requiring primary cesarean delivery (CD). STUDY DESIGN: Morbidly obese women (body mass index ≥40 kg/m(2)) undergoing primary CD at ≥24 weeks' gestation were studied in a secondary analysis of a multicenter registry. Clinical characteristics and outcomes were compared between women who had transverse vs vertical skin incision. The primary outcome was composite wound complication (infection, seroma, hematoma, evisceration, fascial dehiscence) and composite adverse maternal outcome (transfusion, hysterectomy, organ injury, coagulopathy, thromboembolic event, pulmonary edema, death). Multivariable logistic regression analyses were performed to adjust for confounding factors. RESULTS: In all, 3200 women were studied: 2603 (81%) had a transverse incision and 597 (19%) had a vertical incision. Vertical skin incision was associated with lower risk for wound complications (adjusted odds ratio, 0.32; 95% confidence interval, 0.17-0.62; P < .001) but not with composite adverse maternal outcome (adjusted odds ratio, 0.72; 95% confidence interval, 0.41-1.25; P = .24). CONCLUSION: In morbidly obese women undergoing a primary CD, vertical skin incision was associated with a lower wound complication rate. Due to the selection bias associated with utilization of skin incision type and the observational nature of this study, a randomized controlled trial is necessary to answer this clinical question.
Retraction and Revised Conclusion

Am J Obstet Gynecol. 2017 Jul;217(1):85. doi: 10.1016/j.ajog.2017.06.002. Removal notice to The relationship between primary cesarean delivery skin incision type and wound complications in women with morbid obesity: Am J Obstet Gynecol 2014;210:319.e1-4. Marrs CC, Moussa HN, Sibai BM, Blackwell SC. PMID: 28648694
This article has been removed: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been removed at the request of the Editors-in-Chief and Authors. The original publication reported that univariate analysis showed that a vertical skin incision in obese women undergoing Cesarean delivery was associated with a higher odds ratio for wound complications than a transverse skin incision. Multivariable analyses showed a reversal of the association (i.e. the odds of wound complications were lower in women with a vertical skin incision). However, there was an error in the way the variable was entered in the logistic analysis. Re-analysis with the correct coding of the variable indicates that a transverse skin incision is associated with decreased odds of wound complication compared to a vertical skin incision.

Studies Which Show Poorer Outcome with Vertical Incisions in Obese Women
Small Studies Which Show No Statistically Significant Difference
My Previous Writings on Skin Incisions in High BMI Cesareans

Saturday, August 12, 2017

VBAC Prediction Models: Actual Results are Better than Predicted

Original checklist by Melek Speros

Many women with a prior cesarean who want a Vaginal Birth After Cesarean (VBAC) are counseled that they are not "good candidates" for a trial of labor because a VBAC Prediction Model suggests that they have a very low chance of VBAC "success."

In particular, the MFMU VBAC Prediction Model considers weight a strong negative predictive factor for VBAC. As a result, many obese women are told that their chances for VBAC are very low, implying they might as well just sign up for the repeat cesarean now. Many doctors strongly discourage VBAC in women with a high Body Mass Index (BMI). Some hospitals and practices even have BMI restrictions on who is allowed to have a Trial of Labor After Cesarean (TOLAC).

Similarly, many women of color are discouraged from pursuing a VBAC because they are told that they have a lower chance of success. Imagine the negative pressure against VBAC when these two factors intersect in a high BMI woman of color!

However, a recent study from UCLA actually examined how predictive this model was in their institution. They found that it was highly accurate for women predicted to have a very strong chance of VBAC. But to their surprise, they found it was NOT that accurate for women predicted to have a low or moderate chance of VBAC.

The difference was particularly striking for those predicted to have a low chance of a VBAC. 57% of this group actually had a VBAC, when only 29% were predicted to have one, nearly twice the expected rate. 

Of particular note, the authors also documented that, unlike the MFMU prediction model, neither BMI nor ethnicity were associated with lower rates of VBACs in their institution. 

This is especially meaningful to the many women of color and women of size who have been actively discouraged from pursuing a VBAC because of the MFMU prediction model. It also suggests to me that risk perception and the way women are managed in labor (higher induction rates and a lower surgical threshold are common in TOLAC in high BMI women, for example) may influence VBAC "success."

Personally, my VBAC prediction scores were extremely low (22%!) due to multiple risk factors, yet I went on to have not one but two VBACs. If I had let negative predictions discourage me, I would have missed out on my VBACs and their easier recoveries, and I would have been exposed to increased risk for placenta previa and accreta by having additional scars on my uterus.

I know from my work with the International Cesarean Awareness Network (ICAN) that many women are told they have a poor chance at a VBAC and yet go on to have a VBAC anyhow. In fact, few women meet all the "ideal conditions" for VBAC success, yet most will go on to have a VBAC.

If you have been told that you are not a good candidate for VBAC because of your BMI, your race, or various other factors, remember this study and the anecdotal experience of so many women in ICAN. It's okay to consider risk factors, but don't let them overly influence your decision. Group risk factors don't predict what will happen with any one individual. 

No one can guarantee you a VBAC, but neither can anyone reliably predict who will not have a VBAC when given a fair and adequate chance to labor. As the authors conclude in the UCLA study:
As part of efforts to safely decrease cesarean rates in the United States, patients interested in TOLAC (and their providers) should not be discouraged by a low predicted success score.

Reference

AJP Rep. 2017 Jan;7(1):e31-e38. doi: 10.1055/s-0037-1599129. Validation of a Prediction Model for Vaginal Birth after Cesarean Delivery Reveals Unexpected Success in a Diverse American Population. Maykin MM, Mularz AJ, Lee LK, Valderramos SG. PMID: 28255520  Full free text here.
OBJECTIVE: To investigate the validity of a prediction model for success of vaginal birth after cesarean delivery (VBAC) in an ethnically diverse population. METHODS: We performed a retrospective cohort study of women admitted at a single academic institution for a trial of labor after cesarean from May 2007 to January 2015. Individual predicted success rates were calculated using the Maternal-Fetal Medicine Units Network prediction model. Participants were stratified into three probability-of-success groups: low (<35%), moderate (35-65%), and high (>65%). The actual versus predicted success rates were compared. RESULTS: In total, 568 women met inclusion criteria. Successful VBAC occurred in 402 (71%), compared with a predicted success rate of 66% (p = 0.016). Actual VBAC success rates were higher than predicted by the model in the low (57 vs. 29%; p < 0.001) and moderate (61 vs. 52%; p = 0.003) groups. In the high probability group, the observed and predicted VBAC rates were the same (79%). CONCLUSION: When the predicted success rate was above 65%, the model was highly accurate. In contrast, for women with predicted success rates <35%, actual VBAC rates were nearly twofold higher in our population, suggesting that they should not be discouraged by a low prediction score.