An ultrasound of the uterus near term could help doctors determine which pregnant women are good candidates for a “trial of labor” after a previous cesarean delivery.

Results of a Canadian study suggest that using ultrasound to measure the thickness of the lower segment of the uterus towards the end of pregnancy could lead to a significant reduction in uterus rupture among women contemplating vaginal birth after a prior cesarean section.

In the study of 236 women who had a prior cesarean section, researchers found that a lower uterine segment thickness below 2.3 millimeters as seen on ultrasound, combined with a so-called “single-layer muscular closure” in a prior cesarean section, was associated with a “very high risk” of uterus rupture during an attempt at vaginal delivery in women with a history of cesarean section.

These two factors were associated with a 22-fold increased relative risk of uterus rupture during a trial of labor and, when present, “should preclude a trial of labor” in women who’ve had a prior cesarean section, the study team concludes.

The study was presented today at the annual meeting of the Society for Maternal-Fetal Medicine in Washington, DC, by Dr. Emmanuel Bujold from the department of obstetrics and gynecology, Laval University in Quebec.

These results “will help us predict, for patients who have given birth through cesarean section before, which ones are at high risk for uterine rupture during labor in a subsequent pregnancy,” Bujold told Reuters Health.

Using this “very simple and non-expensive measurement,” he concluded, could lead to a “very important” decrease of the risk and potential (problems) associated with vaginal birth after cesarean and, at the same time, “encourage women with prior cesarean to undergo a trial of labor safely.

By Megan Rauscher
NEW YORK (Reuters Health)