Risk Mitigation of VBAC

Ken Turkowski

1 February 1999

I was surprised that, after reading the Flamm/Phalen debate (Volume 53, Number 11 Obstetrical and Gynecological Survey; Point/Counterpoint: I. Vaginal Birth After Cesarean: Where Have We Been and Where Are We Going? Bruce L. Flamm, MD, FACOG; II. The VBAC "Con" Game, Jeffrey P. Phelan, MD, JD), how similar their viewpoints were. In my response to this attempted point/counterpoint, I offer a third percept from a consumer's point of view.

I believe that both Drs. Flamm and Phalen know what needs to be done: (1) adequate disclosure about the risks and benefits of birth options, and (2) reduction of the risks associated with uterine rupture during VBAC.

I like Dr. Phalen's "VBAC Con Game" title, because convincing a patient to deliver by VBAC is to assure her that the probabilities of severe consequences are acceptable. Contrary to the view of OB's of the '80's, I don't consider a 1% chance to be "rare". Coming from an engineering background, I consider 1 chance per million to be "rare", but 1 chance in 100 to be "infrequent".

Can a 1 in a million chance of fetal brain damage be achieved in the modern obstetric delivery setting? If we make the assumption that *no* brain damage occurs if the fetus is delivered within 17 minutes of ominous bradycardia, then achieving the 1 in a million probability can be done by assuring that there is 1/10,000 chance that an emergency cesarean surgical team can be assembled in, say, 10 minutes, with the other 7 minutes used for diagnosing the rupture, administering anesthesia, performing the cesarean incisions, and extracting the fetus (the remaining probability, 1/100, is the probability of uterine rupture).

I view this as close to impossible. The 1/10,000 failure rate for assembling a surgical team seems much too low, given that human and other factors are involved. I suggest a failure rate of 1/100 to 1/500 to be more realistic in a well-prepared tertiary care center, and failure rates as high as 1/10 in more well-prepared, but remote locations.

Are these higher failure rates acceptable? Is it acceptable to have a 1/50,000 to 1/10,000 chance of fetal brain damage in an attempted VBAC delivery in a tertiaty institution? Probably. I would call these rates "improbable" rather than "rare", though. Other complications are likely to have at least as high of a probability of disastrous consequences. How about a 1/1,000 chance of fetal brain damage for the remote locations? I think not. This is still in the "infrequent" class, and not acceptable.

How does one increase the probability of assembling a surgical team? Having only one person available for each role is not enough. It is necessary to have at least 2 people available for each role. It is necessary to have 2-3 operating rooms on site, in case one is busy at the time of need. It is necessary to have kits of instruments and medications packaged and ready to go in each O.R. I conjecture that this, in addition to biweekly "crash cesarean" practice sessions for all personnel, can achieve at least a 9,999/10,000 VBAC/stat-C success rate (1/10,000 failure rate).

Granted, in many institutions, this may actually bring the cost of VBAC up to be in line with that of a cesarean. In institutions with a high delivery rate (i.e. large institutions), there may be negligible differences in cost.

I agree with Dr. Phalen that the patient needs to be better informed, but I can't follow his analogy with GBS cultures. I disagree with Dr. Flamm that "brain damage and death" are too strong to be used in the disclosure. "Injury to the fetus" conjures up images of a scalpal puncture instead. The possibilities of brain damage and death are easier to deal with when the probabilities are remote.

Are cesarean candidates adequately informed of the risks of a C-section? Are they informed of the risks of AIDS and hepatitis if a transfusion is required? What is the risk of hysterectomy? How about the risk of iatrogenic pathology (undoubtedly greater for C-sections than for VBACs, but I doubt whether this is documented as well as it should)?

Probabilities of severe consequences should be compared between VBAC and cesarean deliveries, from both a maternal and fetal viewpoint. Any consent form should include the probabilities of risk for uterine rupture, hysterectomy, transfusion, iatrogenic pathology, etc. for both VBAC and cesarean deliveries. The options for delivery should be presented on an equal basis.

I think that consent forms should come in a two colume format: one for VBACS, and one for cesareans. The benefits of each should be compared side-by-side. The risks of each should be compared side-by-side, along with probabilities thereof. A signature line would appear in each column to indicate the choice. The mother should be allowed to take the form home and discuss it, in order to make an informed decision, rather than being pressured to sign it on the spot.

Neither Drs. Flamm nor Phalen address the subject of diagnosis. A necessary part of achieving the 17 minute "guideline" is to rapidly diagnose that a uterine rupture has occurred. Vigilance is the key. There should always be someone monitoring the FHT, although improved monitoring equipment can reduce the need for additional staff. The papers by Jones, Farmer, Leung, Scott, contain information about diagnosing uterine rupture, the most reliable symptom being prolonged bradycardia.

Improvements to monitoring equipment can reduce the cost of additional staff for monitoring the fetal heart rate. Bradycardia, a lower signal level for the heart rate (i.e. longer period between beats), is trivial to detect with electronic signal monitoring equipment. Variable and late decelerations are nothing more than phase differences between the fetal heart rate and uterine contraction sinusoids, and while not trivial, are still easy to detect electronically. Even beat-to-beat variability can be detected electronically, although this is a tougher task for signal processing equipment.

Until the probabilities of maternal and fetal catastrophe are equalized between VBAC and cesarean delivery, there will always be a tendency for the patient to choose the safer option (which is indicated by Michael McMahon, NEJM 335/10 to be cesarean, by a factor of 2 to 1, for major maternal complications; with other studies, your mileage may vary; are there any others, especially for fetal complications?).

It is my conjecture that the risks associated with VBAC can be reduced by (1) development and deployment of "smarter" monitoring equipment; (2) redundant OR staff, including anesthesia and surgeon; (3) regular emergency response drills;

All of these just cost a little money. However, with the $1000-$2000+ (is this right?) gap between costs of VBAC and cesarean, the money seems to be available.

Suppose the costs and risks of VBAC and cesarean were equalized so that the costs were the same and were each likely to have the same probability of catastrophic consequences: would there still be as strong a campaign to lower the C-section rate?

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last revised: 1/11/05