Sonographic measurement of the lower uterine segment thickness: is it truly predictive of uterine rupture?

BACKGROUND Sonographic examination of the lower uterine segment (LUS) has been used to diagnose a uterine defect and to determine the degree of LUS thinning in women with previous Caesarean section. Previous studies have demonstrated that the LUS thickness measured sonographically has a high negative predictive value for uterine rupture, suggesting that a normal LUS thickness predicts a safe trial of vaginal birth after previous Caesarean section (VBAC). However, the clinical application of LUS measurement in the management of VBAC remains controversial. Because uterine rupture is rare and the number of women willing to attempt VBAC is declining, it would be difficult to recruit sufficient patients for an adequate sample size when designing studies to evaluate LUS measurement in predicting uterine rupture. CASE A healthy 34-year-old, gravida 7, para 5, had a lower segment transverse Caesarean section for her fifth delivery. She underwent a trial of VBAC for her subsequent pregnancy. Despite a normal sonographic LUS evaluation at 37 weeks' gestation, she had uterine rupture during labour. CONCLUSION Clinical experience with the use of LUS measurement in predicting uterine rupture and managing VBAC is limited. Having a national registry to record data and review all cases of uterine rupture would accelerate the accumulation of experience on this subject.