FRIDAY, Jan. 30, 2009 (HealthDay News) -- Measuring the thickness of the uterine scar from a cesarean delivery can help physicians predict which women would be at low risk for uterine rupture and may safely try to have a vaginal delivery, according to a new study by Canadian researchers.
"The thicker the scar is, the stronger the scar is, and the smaller the chance of rupture," said Dr. Emmanuel Bujold, associate professor of obstetrics and gynecology at the University of Laval in Quebec, Canada. Bujold is the lead author of the study, which was expected to be presented Jan. 30 at the Society for Maternal-Fetal Medicine's annual meeting in San Diego.
The issue of repeat cesarean deliveries is of concern, because delivery of a baby by C-section has been linked to higher rates of complications for both mother and infant, Bujold said.
C-section rates have been climbing in the United States and elsewhere. In 2006, about a third of births were by cesarean, with 1.3 million cesarean births and almost 3 million vaginal deliveries, according to the U.S. National Center for Health Statistics.
In deciding which women can safely try a vaginal birth after a C-section, doctors must decide if a vaginal delivery would be safe or if risks -- such as uterine rupture -- would make it unwise.
Bujold's study involved 236 pregnant women who had delivered previously by C-section but who planned a vaginal delivery. They used ultrasound to measure the lower part of the uterus, which correlates with scar thickness from the previous C-section, and then followed the women through their deliveries.
During labor and delivery, three of the women had a complete uterine rupture. In six, the scar reopened. Women who had uterine rupture had a very thin scar, Bujold said.
"We found the cutoff is probably 2.3 millimeters" in terms of scar thickness, he said. The average risk of rupture is about 1 percent, Bujold said, but in the study, "if you had a scar smaller than 2 mm, your risk of rupture [was] about 10 percent."
Measuring the uterine scar is very common in France and in Quebec, Bujold said, and is becoming more common in the United States.
The study confirms results published in 1996 that also found that uterine rupture and uterine scar opening during labor could be predicted by ultrasound measurements of the previous scar.
Bujold suggested that measuring the scar could predict who would be and would not be at risk for uterine rupture and could help physicians decide which women would be candidates for a vaginal delivery.
Dr. Shoshana Haberman, director of perinatal testing services at Maimonides Medical Center in Brooklyn, N.Y., said she has been doing this measurement on women with previous C-sections for a few years. And while the new study results are interesting, she said, the prediction method is not yet definitive.
"We need more data -- that's the bottom line," Haberman said. "We need more data to decide the cutoff."
The ultrasound measure is also operator-specific, she added, so it could vary from person to person.
Another expert welcomed the study, saying it confirms the previous research.
"Not all women with previous C-sections are created equal," said Dr. Alessandro Ghidini, a maternal-fetal medicine specialist in Alexandria, Va., and president of the scientific committee for the meeting at which the study was being presented.
Taking into account the measurement, plus other factors -- including the reason for the previous C-section -- will help a woman and her doctor decide the best course for the current pregnancy, he said.
Though the test is not done as often in the United States as elsewhere, he said, women who've had a cesarean delivery could ask their doctors about having the test.
More information
The U.S. Centers for Disease Control and Prevention have more on a healthy pregnancy.
