I. Can ultrasound identify scar in mid to late pregnancy? Since there is no difference in the sonographic performance between the scar and the lower uterine muscular layer in mid- to late-term pregnancy, ultrasound cannot accurately identify the boundary between the scar and the muscular layer in the lower uterine layer in mid- to late-term pregnancy, and therefore cannot correctly measure the thickness of the scar. The fact that the fetal previa partially affects the display of the scar in late pregnancy and the presence of lateral echogenic attenuation of the ultrasound beam makes the true scar location difficult to measure. From the above technical aspects, there is no sufficient theoretical basis for ultrasound measurement of scar thickness in late pregnancy. Second, how feasible is the measurement of the lower uterine segment? Since scar cannot be accurately determined in clinical practice, how feasible is the measurement of the lower uterine segment? There are many relevant literatures exploring the thickness of the lower uterine segment with a history of cesarean delivery, however, summarizing most of the literature, the opinions reached are: first, there is no data to confirm that the difference in the thickness of the lower uterine segment between the normal and cesarean population is statistically significant; second, the measurement of the lower uterine segment cannot be standardized because the measurement site of the lower uterine segment cannot be unified, and the measurement is also influenced by the degree of bladder filling, etc., making it impossible to standardize the measurement The reproducibility of measurement data is poor, which directly affects its application value. Third, is the thickness of the lower segment related to uterine rupture? Reviewing the published literature on the correlation between the measurement of lower uterine segment thickness and uterine rupture in mid to late pregnancy, the overall conclusions are: 1. There are many factors influencing the rupture of the scarred uterus, and the strength of the scar and the tension to which the scar is subjected need to be considered. 2, There is no clear correlation between ultrasound measurement of the thickness of the lower uterine segment during pregnancy and the strength of the scar, as well as the actual thickness of the lower uterine segment. 3, The method of ultrasound measurement of the thickness of the lower uterine segment (myometrium) cannot be standardized. 4. There is no clear cut-off value for the thickness of the lower segment that can predict uterine rupture. 4. What are the risk factors for uterine rupture? The factors associated with uterine rupture in a second pregnancy with scarred uterus reported in a larger sample of literature include: time interval between pregnancies and deliveries, suturing method of cesarean delivery, fetal weight, experience of vaginal delivery, whether to induce labor and oxytocin dose, etc.; non-associated factors include: gestational week, maternal age, race, whether eclampsia is a complication or comorbidity, twin births or not, labor duration, whether epidural anesthesia or not. In summary, there were 10 cases of complete uterine rupture at the First Hospital of Sun Yat-sen University in the past 8 years, most of which had a history of myomectomy, and only one case had a history of cesarean section + myomectomy, and the rupture site was at the posterior wall rather than the scar. Personally, I think that the rupture of a scarred uterus with a history of myomectomy should be more clinically significant than that of a scarred uterus with a history of cesarean delivery. Conclusion: Relationship between uterine scar thickness and uterine rupture in late pregnancy: 1. Ultrasound cannot accurately distinguish the uterine scar from the myometrial boundary in mid to late pregnancy. 2, There is no sufficient data to confirm the accuracy of ultrasound measurement of the lower uterine segment thickness in mid- and late-term pregnancies. 3, Uterine scar thickness is not related to elasticity and tension (thin does not necessarily break, broken does not necessarily thin) 4, The available literature with more rigorous design does not confirm that scar measurement can predict uterine rupture, in fact it is simply impossible to avoid medical ethics to conduct a randomized controlled study to predict what kind of scar will rupture. 5. Most of the uterine ruptures that occur clinically during pregnancy are in pregnancies after removal of larger fibroids, and there is a lack of randomized controlled studies to determine whether the thickness of the myometrium is associated with rupture. There is no clear and effective prediction method for the risk of uterine rupture in second pregnancies in scarred uteri with either a history of cesarean delivery or a history of larger myomectomy, and further data need to be summarized. However, routine measurement of lower uterine segment thickness is not recommended to avoid unnecessary clinical confusion.