CONTROVERSIES IN OB/GYN

VBAC: Is it worth the risk?

By Michael F. Greene, MD

No. Patients should have the option of elective repeat C/S.

Every medical student is taught early in his or her career the basic principle that no tissue heals to produce a scar that is as strong as the native tissue was before it was disrupted. This is true despite our best efforts at surgical repair and pertains to skin, fascia, bone, and uterine muscle. Thus, it should come as no surprise when hysterotomy scars from cesarean deliveries rupture in subsequent pregnancies. Douglas recognized this 40 years ago in a series from the New York Lying-In Hospital.¹ At that time, the overall C/S rate was 4% and the indication for half of the procedures was a prior C/S.

Historical trends

Of the more than 2,000 women with prior C/S scars in Douglas's study, just over 1% had uterine ruptures during labor and more than a third of their fetuses died. Douglas concluded that, "Probably the most vehement objections to the policy of vaginal delivery after cesarean section allude to the occurrence of catastrophic ruptures of the uterine scar." That kind of experience and reason, coupled with the dogmatic but mellifluous mantra of "once a cesarean section, always a cesarean section," cast the practice of vaginal birth after cesarean (VBAC) into disrepute for decades.

Subsequently, C/S went from commonplace to epidemic, with the United States national rate peaking in the late 1980s at nearly 23%.² Those concerned with the potential morbidity, mortality, and financial implications of the rising C/S rate encouraged reconsideration of VBAC. Enthusiastic reports of success and optimistic assessments of meta-analyses propelled the VBAC juggernaut.^3-5 But these studies soon were followed by reports of maternal and perinatal morbidity and mortality associated with VBAC, most of which were attributable to uterine ruptures.^6-8

A closer look at the data

Mozurkewich and Hutton examined a number of maternal and fetal outcome measures in their meta-analysis of 11 studies with 39,000 subjects.⁹ They calculated statistically significant increases in risks for uterine rupture (odds ratio [OR] 2.1), Apgar score less than 7 at 5 minutes (OR 2.2), and fetal death (OR 1.7) (58 vs 34/10,000) associated with a trial of labor as compared to elective repeat C/S. On the other hand, these authors found significantly lower risks for maternal febrile morbidity (OR 0.7), transfusion (OR 0.6), and hysterectomy (OR 0.4). It is important to emphasize that these data, like all those collected to date, was observational from the results of clinical practice and not from randomized trials. The findings of increased risks for transfusion and hysterectomy with elective C/S likely are due to patient selection (for example, known placenta previa, suspected accreta, multiple prior C/S rather than only one) because they are not driven by uterine ruptures, which are more common with a trial of labor. Maternal mortality is thankfully so low that even with 44,000 deliveries, there were too few deaths to permit a statistically meaningful comparison between the two groups. It is notable that the only deaths (three) were in the trial-of-labor group and the maximum risk of maternal mortality in the elective C/S group is approximately 1.1/10,000. The potential for serious complications in future pregnancies, including potentially life-threatening problems such as placenta accreta with multiple C/S, was not directly addressed. This would obviously not be a concern for women not planning future pregnancies.

Recently, Smith found the risk of perinatal mortality associated with a trial of labor (12.9/10,000) among more than 300,000 women in Scotland to be 11 times higher (OR 11.6) than with elective repeat C/S (1.1/10,000).¹⁰ After adjusting for other factors that might contribute to this difference, he estimated that 91% of the difference in risk was directly attributable to the increased risk of death associated with the trial of labor. Neither the meta-analysis nor the Scottish study had data to address the risk of perinatal survival with cerebral palsy (CP) as the result of an intrapartum asphyxic event associated with a uterine rupture. Some authors have estimated that risk to be 2–3/10,000.^11,12

The issue of informed consent

The process of obtaining informed consent for medical care requires that physicians provide patients with information that a reasonable person would want to know under the circumstances. Most reasonable people would want to know that VBAC is associated with a greater risk of perinatal mortality than elective repeat C/S. While conceding the truth of this statement, many point out that the difference is small, and that the potential benefits of a successful VBAC are worth the small increase in risk. Mozurkewich has argued that "VBAC [is] safer than you think."⁹ Based upon the data in her meta-analysis, she estimated that between 693 and 3,332 C/S need to be done to prevent one perinatal death. A similar calculation using Smith's Scottish data yields a comparable number (847).¹⁰ Both of these estimates would be somewhat smaller if prevention of cases of CP also was considered.

Conclusion

Much has been made of the different ways that physicians can present risk to patients, such as apparently imposing relative risks ("11 times higher") versus apparently small absolute risks ("5.8 per 1,000"). The issue, however, should not be how the doctor presents the data but rather how the patient perceives the information, to whom the risks accrue—mother or fetus—and who makes the decision for the patient. How should a woman balance the reduced risk of febrile morbidity and a shorter hospital stay for herself against the increased risk of death for her fetus? Some patients view the absolute numbers for risks of perinatal death for VBAC versus repeat C/S as very small, even indistinguishable, and well worth taking for the potential benefits associated with successful VBAC. Other women will question whether there is a way to reduce the risk of perinatal death even further. For them, the answer must be, "Yes, elective repeat C/S."

REFERENCES

1. Douglas RG, Birnbaum SJ, MacDonald FA. Pregnancy and labor following cesarean section. Am J Obstet Gynecol. 1963;86:961-971.

2. Martin JA, Hamilton BE, Ventura SJ. et al. Births: final data for 2000. National Vital Statistics Reports. Vol. 50, No. 5. Hyattsville, Md: National Center for Health Statistics; 2001.

3. Martin JN Jr, Harris BA Jr, Huddleston JF, et al. Vaginal delivery following previous cesarean birth. Am J Obstet Gynecol. 1983;146:255-263.

4. Phelan JP, Clark SL, Diaz F, et al. Vaginal birth after cesarean. Am J Obstet Gynecol. 1987;157:1510-1515.

5. Rosen MG, Dickinson JC, Westhoff CL. Vaginal birth after cesarean: a meta-analysis of morbidity and mortality. Obstet Gynecol. 1991;77:465-470.

6. Scott JR. Mandatory trial of labor after cesarean delivery: an alternative viewpoint. Obstet Gynecol. 1991;77:811-814.

7. Farmer RM, Kirschbaum T, Potter D, et al. Uterine rupture during trial of labor after previous cesarean section. Am J Obstet Gynecol. 1991;165:996-1001.

8. McMahon MJ, Luther ER, Bowes WA Jr, et al. Comparison of a trial of labor with an elective second cesarean section. N Engl J Med. 1996;335:689-695.

9. Mozurkewich EL, Hutton EK. Elective repeat cesarean delivery versus trial of labor: a meta-analysis of the literature from 1989 to 1999. Am J Obstet Gynecol. 2000;183:1187-1197.

10. Smith GC, Pell JP, Cameron AD, et al. Risk of perinatal death associated with labor after previous cesarean delivery in uncomplicated term pregnancies. JAMA. 2002;287:2684-2690.

11. Grobman WA, Peaceman AM, Socol ML. Cost-effectiveness of elective cesarean delivery after one prior low transverse cesarean. Obstet Gynecol. 2000;95:745-751.

12. Clark SL, Scott JR, Porter TF, et al. Is vaginal birth after cesarean less expensive than repeat cesarean delivery? Am J Obstet Gynecol. 2000;182:599-602.

Dr. Greene is Director of Maternal-Fetal Medicine, Massachusetts General Hospital, Boston, Mass.

Reader Response Form

VBAC: Is it worth the risk?

What's your call on the controversy presented by Drs. Simpson and Greene? Let us know and learn later how your view compares with those of others when we print a sampling of reader responses.

Yes. Repeat C/S is not mandatory for all.

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No. Patients should have the option of elective repeat C/S.

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Michael Greene. VBAC: Is it worth the risk?

Contemporary Ob/Gyn

Dec. 1, 2003;48:27-34.