Risks Associated With VBAC Small

A new study of women who had previously undergone cesarean-section deliveries, but who later chose vaginal delivery for subsequent births, should calm the concerns of expectant mothers and their obstetricians. While serious complications are possible, the absolute risk of these occurring is very small.
VBACs: A hotly-debated issue
This study provides the latest evidence for an ongoing quandary for pregnant women and their obstetricians. For years, doctors recommended that women who delivered via cesarean section should not deliver future infants vaginally. But studies over the past 20 years disputed that belief, and many women have chosen to undergo VBAC, or vaginal birth after cesarean section. This new four-year study is one of the largest ever performed to provide physicians and women with information on one of the most debated issues in maternity care.

"Available data comparing outcomes of a trial of labor and an elective repeat operation have been inadequate. This new data will be valuable to medical professionals who counsel women who are considering their options for childbirth following cesarean delivery," says Dr Mark Landon, vice chairman of obstetrics and gynecology at The Ohio State University Medical Center and principal investigator for the 19-academic center study.

The study demonstrated that, when compared to elective repeat cesarean delivery, women attempting vaginal birth after cesarean section (VBAC) are at increased risk for maternal morbidity and serious obstetric complications, such as uterine rupture, endometritis, transfusion, or newborn hypoxic ischemic encephalopathy (newborn brain injury due to lack of oxygen).

Researchers at 19 academic medical centers joined forces to complete the research, which included cases between 1999 and 2002. Of the approximately 46,000 women in the study with a prior cesarean delivery, one in three, or about 16,000, underwent elective, repeat cesarean delivery without labor. Another 18,000 attempted VBAC, while approximately 12,000 women had other maternal or fetal indications for a repeat cesarean delivery.

About 39 percent of the women chose to attempt a vaginal delivery in spite of their previous cesarean section. Of these, 73 percent succeeded in this "trial of labor." Symptomatic uterine rupture -- one of the major risks in such situations -- occurred in less than 1 percent (128 women or 0.7 percent) of these cases.

Among infants whose mothers chose this "trial of labor," the frequency of hypoxic ischemic encephalopathy (HIE) -- another serious complication -- was increased. While only 13 cases of HIE occurred with "trial of labor" cases, there were no cases among women who had elected to have a repeat cesarean delivery. Eight of 13 cases of HIE, including two neonatal deaths, followed by uterine rupture. Maternal morbidity, endometritis and blood transfusion were all more likely among women who chose VBAC than among those who chose repeat cesarean delivery.

"While the magnitude of these risks is small, women who have had a previous cesarean section and who are considering choices for childbirth should be aware of the level of risk involved," says Dr Landon. "Overall, the risk for a serious newborn complication is approximately 1 in 2,000 trials of labor. At this level of risk, many women will continue to opt for an attempted VBAC."

In the United States, the overall rate of cesarean delivery has risen dramatically, from 5 percent in 1970 to five times that (26.1 percent) in 2002. During the last 25 years, as repeat cesarean birth became the leading reason for abdominal delivery, studies detailed the relative safety of VBAC. The rate of VBAC in the United States increased 10-fold, from 3 percent in 1981 to 31 percent in 1998, Dr Landon says. But the safety and appropriateness of widespread adoption of VBAC has been challenged. Dr Landon says there has been an apparent rise in the frequency of reported uterine rupture among pregnant women, with associated maternal and perinatal risk. The rate of VBAC fell by more than half to 12.7 percent in 2002.

In past studies of VBAC and cesarean sections, the magnitude of risks has remained uncertain; the terminology and definitions for uterine rupture have varied significantly; and the lack of direct evidence about benefits and risks has made it difficult for physicians to provide appropriate counseling. The picture has been anything but clear. In addition, liability concerns have led physicians and hospitals to limit VBAC as an option, Dr Landon says.

"There are important distinctions in this study," he notes. "Almost all existing data until now came from large retrospective studies, which are subject to many biases. This study was prospective in gathering data and underwent intensive review. It is important to share this new data with women regarding childbirth choices." PregnancyAndBaby.com

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