In a study presented at the Society for Maternal-Fetal Medicine's (SMFM) annual meeting, researchers unveiled findings that show that by using a sonogram to measure the lower uterine segment (LUS) thickness, they can predict uterine scar defects in women who had previous cesarean deliveries and anticipate which patients are at risk for subsequent uterine rupture if they have a trial of labor.

The Centers for Disease Control's Web site lists statistics from the National Vital Statistics System that show that there has been a sharp increase in the number of cesarean births. "Preliminary data for 2005 indicate that 30.2% of all live births in the United States were cesarean deliveries, marking the highest U.S. total cesarean rate ever reported. Since 1996, the total cesarean rate has increased by 46%, driven by both an increase in the percentage of all women having a first cesarean and a decline in the percentage of women delivering vaginally after a previous cesarean."

Repeat cesarean deliveries are an obvious concern. "There is a growing concern about the increase in cesarean births because there is a body of evidence showing that they are associated with higher rates of maternal and infant complications," said Emmanuel Bujold, M.D., with the Department of Obstetrics & Gynecology, Faculty of Medicine, Universite Laval, Quebec. "There are far fewer complications to the mother and infants as a result of a vaginal birth," he continued, "So it is important to determine when a patient with a history of prior cesarean section can have a vaginal birth safely."

The study looked at 236 women who had a prior cesarean delivery. Their LUS thickness was measured between 35 and 38 weeks of gestation. Three cases of complete uterine rupture and six cases of uterine scar dehiscence were reported. Analysis demonstrated significant associations between the risk of uterine rupture during trials of labor and full LUS thickness. The combination of full LUS thickness under 2.3mm and a single-layer muscular closure was significantly associated with uterine rupture (relative risk: 21.8, 95% CI: 2.1-222, p,