COLUMBUS – The most definitive study to date of women who had previously undergone cesarean-section deliveries, but who later chose an attempt at vaginal delivery for subsequent births, shows that serious complications are possible, but that the absolute risk of these occurring is very small.
These new findings will appear this week in the current issue of the New England Journal of Medicine.
The multicenter study was sponsored by the National Institute of Child Health and Human Development Maternal Fetal Medicine Units Network – a part of the National Institutes of Health.
“This study is significant in addressing an issue that continuously receives debate in obstetrics,” said Mark Landon, vice chairman of obstetrics and gynecology at The Ohio State University Medical Center and principal investigator for the four-year study. “Until now, the information comparing a trial of labor and an elective repeat operation has been inadequate to counsel women concerning their options for childbirth following prior cesarean delivery.”
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 “vaginal birth after cesarean section,” (VBAC), while approximately 12,000 women had other maternal or fetal indications for a repeat cesarean delivery.
The study demonstrated that, when compared to elective repeat cesarean delivery, women attempting 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).
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” and delivered vaginally. Symptomatic uterine rupture - one of the major risks in such situations - occurred in less than 1 percent (124 women or 0.7 percent) of these cases.
The study also confirmed that an increased risk of uterine rupture accompanied labor induction, which was evident regardless of the method of induction employed.
Among infants whose mothers chose this “trial of labor,” the frequency of hypoxic ischemic encephalopathy (HIE) – another serious complication—was increased. While only 12 cases of HIE occurred with “trial of labor” cases, there were no cases among women who had elected to have a repeat cesarean delivery. Seven of 12 cases of HIE, including two neonatal deaths, followed 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 for serious complications 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,” said Landon. “Overall the risk for a serious newborn complication is approximately 1 in 2000 trials of labor. At this level of risk, many women will continue to opt for an attempted VBAC. The benefits of this approach would be faster recovery, shorter hospital stay and avoiding the risks of major surgery.”
In the United States, the overall rate of cesarean delivery has risen dramatically, from 5 percent in 1970 to more than five times that (27 percent) in 2003. During the last 25 years, as repeat cesarean birth became the leading reason for abdominal delivery, studies detailed the relative safety of VBAC and suggested increasing the VBAC rate would be crucial to lowering the overall rate of cesarean delivery. The rate of VBAC in the United States increased 10-fold, from 3 percent in 1981 to 31 percent in 1998, Landon said.
But the safety and appropriateness of widespread adoption of VBAC has been challenged. Landon said there has been an apparent rise in reported uterine rupture among pregnant women, with associated maternal and perinatal risk. More reports have appeared in the literature, but actually the rupture rate has been fairly constant: 0.5 – 1.0 percent of trials of labor. The rate of VBAC fell by more than half to 10.6 percent in 2003. In addition, liability concerns have led physicians and hospitals to limit VBAC as an option, Landon said.
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.
“There are important distinctions in this study,” Landon noted.
“Existing data until now has largely come from retrospective studies, utilizing birth certificate data which is often unreliable. This study was prospective in gathering data by trained nursing personnel and underwent central renew by the investigators for cases of uterine rupture. This is particularly important with respect to the fetal outcomes associated with uterine rupture. It is important to share this new data with women regarding childbirth choices.”
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