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.
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