This study aimed to estimate the occurrence of uterine rupture during trial of labor after cesarean delivery when lower uterine segment thickness measurement is included in the decision-making process about the route of delivery.
In 4 tertiary-care centers, we prospectively recruited women between 34 and 38 weeks of gestation who were contemplating a vaginal birth after a previous single low-transverse cesarean delivery. Lower uterine segment thickness was measured by ultrasound imaging and integrated in the decision of delivery route. According to lower uterine segment thickness, women were classified in 3 risk categories for uterine rupture: high risk (<2.0 mm), intermediate risk (2.0–2.4 mm), and low risk (≥2.5 mm). Our primary outcome was symptomatic uterine rupture, which was defined as requiring urgent laparotomy. We calculated that 942 women who were undergoing a trial of labor after cesarean delivery should be included to be able to show a risk of uterine rupture <0.8%.
We recruited 1856 women, of whom 1849 (99%) had a complete follow-up data. Lower uterine segment thickness was <2.0 mm in 194 women (11%), 2.0–2.4 mm in 217 women (12%), and ≥2.5 mm in 1438 women (78%). Rate of trial of labor was 9%, 42%, and 61% in the 3 categories, respectively (P<.0001). Of 984 trials of labor, there were no symptomatic uterine ruptures, which is a rate that was lower than the 0.8% expected rate (P=.0001).
The inclusion of lower uterine segment thickness measurement in the decision of the route of delivery allows a low risk of uterine rupture during trial of labor after cesarean delivery.