My daughter, who turns two years old in June, is becoming something of a medical rarity. This isn’t because she is showing signs of a late-developing handicap or extraordinary ability for her age – it’s because she came into the world as a vaginal birth after Cesarean section (VBAC), delivered by a certified nurse midwife.

Although more than three-quarters of women who choose a trial of labor over a repeat Cesarean section successfully deliver vaginally, studies showing slightly elevated risks of rupture or infection of the uterus with VBAC, pressure from insurance companies concerned about lawsuits, and restrictive medical guidelines discourage most women from even trying.

After reaching a high in 1996 of 28.3 percent of women who previously delivered by Cesarean, the national VBAC rate today is fewer than 1 in 10. As a result of all of these repeat Cesareans, 1 in 3 births in the U.S. today occur by Cesarean.

For the past two days, a conference at the National Institutes of Health has sought to understand the reasons for the decline of VBAC, and what might be done to reverse what most believe to be a negative trend. An independent panel will release a draft statement summarizing the take-home points from the conference. What the statement probably won’t say, but what I believe to be a large part of the truth, is that the U.S. has such a low VBAC and high Cesarean rate because obstetricians deliver most of our babies, and obstetricians aren’t primary care clinicians.

The old medical maxim “when you hear hoofbeats, think horses, not zebras” refers to the fact that common conditions are more likely to present than rare or estoteric conditions. A dry cough, for example, is more likely to be due to allergies than Erdheim-Chester disease. Vomiting and diarrhea are much more likely to be caused by rotavirus than Vibrio vulnificus.

Primary care clinicians internalize this maxim during their community-based training programs; specialist physicians – who spend most of their training learning to diagnose and treat “zebras” at academic medical centers where patients with uncommon conditions are referred for care – typically abandon it early on. And even though many women visit obstetricians for routine gynecologic care, when it comes to the primary care-specialist attitude divide, Ob/Gyns come down clearly on the side of the specialists.

I could offer lots of anecdotes about why the above is true from having worked with OB/GYN physicians throughout medical school and residency training (when I delivered more than 80 babies and assisted in about half as many Cesarean sections), but objective data support the notion that labor managed by family physicians and professional midwives is considerably more likely to result in a vaginal birth than labor managed by an obstetrician, even controlling for factors such as maternal age and risk status.

It isn’t difficult to understand why. If an obstetrician is feeling uncertain about how well a patient’s labor is progressing and has an inflated estimate of the probability that something might go wrong (the zebra), it’s very hard to resist the temptation to eliminate the uncertainty by delivering the baby surgically, then and there. On the other hand, if the surgeon is at least a phone call away (the American Academy of Family Physicians’ 2005 guideline on trial of labor after Cesarean noted that there’s no good evidence that having a 24-hour on-call surgeon and anesthetist in-house improves maternal or infant outcomes), the family physician or nurse midwife might be more patient with the hoofbeats, betting they’re hearing a horse.

And, in fact, in a 2004 study of nearly 18,000 women who attempted VBAC, the most feared complication of uterine rupture (which requires an emergency Cesarean), occurred in less than 1 percent of cases. As mentioned earlier, a trial of VBAC is successful more than 75 percent of the time.

It’s a real shame that women in the U.S. are discouraged from attempting them more often.

Kenneth Lin is a family physician who blogs at Common Sense Family Doctor.

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