WINSTON-SALEM, N.C. – For a pregnant woman who already has had one cesarean delivery, an attempt at vaginal delivery is more dangerous for the baby than a second cesarean section, according to a research study at 19 academic health centers, including Wake Forest University Baptist Medical Center.
The study, published in today's New England Journal of Medicine, showed that vaginal birth after a cesarean section (VBAC) also is more dangerous for the mother, leading to the increased possibility of a ruptured uterus and such complications such as endometritis – infection of the uterus – and the need for transfusions.
"This information is relevant for counseling women about their choices after a cesarean section," said the researchers, who included Margaret A. Harper, M.D., of Wake Forest Baptist. The 19 academic health centers all belong to the Maternal-Fetal Medicine Units Network of the National Institute of Child Health and Human Development.
The issue is important because of the debate about the overuse of cesarean sections, which reached 26 percent of all births in 2002. The U.S. Public Health Service has been seeking a reduction in the rate of cesareans to 15 percent; and had set a goal that 37 percent of women who previously had had a cesarean section to try normal – or vaginal – delivery for the next child.
"This study shows that the risk of adverse perinatal outcomes is increased with a trial of labor after a prior cesarean delivery but also confirms that the risk is still very small," said Harper, associate professor of obstetrics and gynecology. "Therefore, the members of the network conducting this study recommend thorough counseling of women interested in VBAC, but have not recommended abandoning VBAC."
She said that an important issue is the number of future pregnancies desired. "The risks of complications before and during delivery increase with increasing numbers of cesarean operations," she said. The lead author is Mark B. Landon, M.D., of Ohio State University. For the study the researchers monitored all pregnant women at the 19 centers during a four-year period who had had a cesarean section and were carrying a single child – 45,988 women in all. Of those, 17,898, or 38.9 percent, elected to try normal delivery, and 15,801, or 34.4 percent, elected a second cesarean. Of the rest, 9,011 had medical reasons to have a second cesarean, and 3,276 were already in labor when they arrived at the hospital.
The results showed that the rate of uterine rupture was seven per 1,000 among the mothers who were attempting vaginal delivery, compared with no uterine ruptures among the women who chose a second cesarean. Endometritis developed in 2.9 percent of the women who chose normal delivery, compared to 1.8 percent of the women who elected a second cesarean; of the women who elected normal delivery, 1.7 percent required a transfusion, compared to 1 percent of those in the cesarean group.
The researchers said the results indicate that in about one in 2,000 cases, the baby would be affected adversely – during or after the attempt at normal delivery. The researchers said the risk "is quantitatively small but greater than that associated with elective repeated cesarean delivery."
The researchers found that one complication of birth – insufficient oxygen supply to the brain that can lead to acute brain injury "was significantly greater among the infants of women who underwent a trial of labor" than among the infants of women who elected a second cesarean. "The rate was eight per 10,000 in the attempted vaginal delivery group and no cases in the elective repeat cesarean delivery group," Harper said.
The researchers noted, "It has generally been accepted that vaginal delivery is associated with lower maternal morbidity and mortality rates than is cesarean section." But the instances of infection or inflammation of the wall of the uterus and the increased rate of transfusion mitigate that advantage.
"During the past 25 years, as the number of repeated cesarean sections grew, vaginal birth after cesarean section was increasingly recommended in clinical-management guidelines, prompting a rise in the use of this approach in the United States from 3 percent of deliveries after a cesarean section in 1981 to 31 percent in 1998."
Increasing concern about the risk of uterine rupture and the health of both the mother and the baby led to a sharp decline in VBAC to 12.7 percent in 2002. The new study was aimed at providing scientific evidence on which approach was better.
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