A report of the study done at 19 academic
medical centers, including the University of Cincinnati, appears in the
Dec. 16 issue of The New England Journal of Medicine.
One of the major risks in vaginal birth
after cesarean section (VBAC) is symptomatic uterine rupture. Although
it occurred in less than 1 percent (124 women or 0.7 percent) of VBAC
cases, the study confirmed an increased risk of uterine rupture,
regardless of the method of induction employed.
This, according to UC's Baha Sibai, MD,
is the most significant aspect of the study. Women should know that if
they opt for "trial of labor" after a previous cesarean section, they
risk causing brain damage to their baby in the event of a uterine
While the risk to the mother is about the
same with cesarean section and trial of labor, and the risk of uterine
rupture and subsequent fetal brain damage is low, Dr. Sibai says, "It's
very difficult to understand why any patient would accept it."
Dr. Sibai, chairman of UC's Department of
Obstetrics and Gynecology, participated in the study both in his
current position in Cincinnati and at his previous appointment at the
University of Tennessee.
Conducted between 1999 and 2002, the
study involved about 46,000 women who had undergone prior cesarean
delivery. About 16,000 of these women underwent elective, repeat
cesarean delivery without labor, another 18,000 attempted VBAC, and
about 12,000 more had other maternal or fetal indications for a repeat
The study results showed that compared
with elective repeat cesarean delivery, women attempting VBAC are at
increased risk for maternal morbidity and serious obstetric
complications, such as uterine rupture, endometritis, and transfusion
or newborn hypoxic ischemic encephalopathy (HIE), a type of 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 trial of labor and delivered vaginally.
Among infants whose mothers chose trial
of labor, the frequency of hypoxic ischemic encephalopathy was
increased. While only 12 cases of HIE occurred with labor, there were
no cases among women who 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.
"This study is significant in addressing
an issue that continuously receives debate in obstetrics," says Mark
Landon, MD, principal investigator for the four-year study and vice
chairman of obstetrics and gynecology at Ohio State University Medical
"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
"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," Dr. Landon says. "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. The benefits of this approach would be faster recovery,
shorter hospital stay and avoiding the risks of major surgery."
In past studies of VBAC and cesarean
sections, the risk has remained uncertain. Terminology and definitions
for uterine rupture 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," says Dr. Landon.