Ultrasound diagnosis of defects in the scarred lower uterine segment during pregnancy.

A prospective study was begun using ultrasound to diagnose defects in the lower uterine segment. Seventy patients were examined and delivered by cesarean section, including 58 at risk because of previous cesarean section and 12 nulliparous controls not at risk. Of the at-risk patients, 12 had confirmed defects, for an incidence of 20.7%. All the controls were normal. The false-positive rate for at-risk patients was 7.1%, and the positive and negative predictive values were 92.3 and 100%, respectively. For the diagnosed cases, the sonographic lower uterine segment seemed to form earlier (P less than .01) and was thinner (P less than .01) than that in the negative cases or the controls. Although our study design was observational and did not allow us to test the performance of the lower uterine segment when a defect was found, we discuss the use of a three-stage classification system to assist in identifying sonographically detected defects in a future trial of labor protocol. We conclude that sonographic surveillance is a reliable and practical means of evaluating the lower uterine segment after conception and before labor or delivery.