Importance: Uterine rupture during labor is a calamitous event that can result in maternal/neonatal morbidity/ mortality. Lower uterine segment (LUS) thickness measurement is a proposed method to determine the risk factor of uterine rupture in women undergoing trial of labor after cesarean. Does this measurement predict uterine rupture risk?Objectives: This review examines current evidence to determine if a thin LUS ultrasound diagnosis during pregnancy with prior cesarean delivery(s) can reliably predict uterine rupture risk while attempting vaginal birth after cesarean (VBAC).Evidence Acquisition: Electronic databases (PubMed and CINAHL) were searched with one limitation of abstracts in English. Search terms used were "lower uterine segment" AND "risk(s)" AND "rupture" OR "dehiscence.Results: After reviewing 164 identified articles, 15 were used in this review. Of the studies including LUS thickness measurement, notable differences were found: gestational age at time of measurement, full thickness measurement versus myometrial thickness, number of sonographers involved, ultrasound technique (transabdominal vs transvaginal), and blinding. Other factors influencing LUS thickness include fetal weight, amniotic fluid volume, and gestational age. The most recent systematic review and meta-analysis suggests that an LUS > 3.65 mm should be safe for a VBAC, 2-3.65 mm is probably safe, and <2 mm identifies a patient at higher risk for uterine rupture/dehiscence.Conclusions: Study heterogeneity, absence of an agreed upon thickness threshold, poor correlation between ultrasound and MRI measurements, or physical cesarean measurements currently make VBAC uterine rupture risk prediction uncertain.Relevance: Our aim is to analyze existing literature to determine if evidence supports LUS measurement in women undergoing VBAC after cesarean to determine risk of uterine rupture.Target Audience: Obstetricians and gynecologist, family physicians Learning Objectives: After completing this learning activity, the participant should be able to identify the differences and how they occur between studies evaluating the thinness of the LUS in women undergoing a trial of labor after cesarean delivery; compare the accuracy of LUS measurement between ultrasound, MRI, and physical measurement at cesarean delivery; and describe the factors that influence the thinness of the LUS.Uterine rupture is an acute catastrophic event that mandates a timely diagnosis and immediate operative intervention for the best maternal/fetal outcome. Although an uncommon even during labor with an incidence of 22/10,000 births, uterine rupture is one of the true obstetric emergencies. 1 All authors, faculty, and staff have no relevant financial relationships with any ineligible organizations regarding this educational activity.