Transvaginal sonographic assessment of previous cesarean section scar in late pregnancy in correlation with intra operative scar condition

The cesarean section rates increased over 40 years from about 5% to rates well above and kept going up after a short period of decline in the late 80’s to mid 90 ’s. The cesarean section rate exceeds 29% in recent surveys in the US and is even increase is not only medical but also social, financial as well as medicolegal. Attempted vaginal birth after previous cesarean section (VBAC) remains controversial. Although it has been reported as safe and has contributed to a reduced cesarean delivery rate. yet it is associated with a risk of uterine rupture. The rate of uterine rupture varies according to the type and location of the cesarean incision. Because the fetal and maternal consequences of uterine rupture can be serious and life threatening, the proper selection of patients would be an important prerequisite.Objectives: The aim of this study is to assess the utilization of transvaginal ultrasound to evaluate the thickness of the lower uterine segment in patients with history of previous cesarean section during late pregnancy and correlation with intraoperative assessment of the scar. This might have an impact on decision-making about the mode of delivery.Patients and methods: We measured the lower segment thickness from the muscularis and mucosa of the bladder on the outer side to the chorioamniotic membrane inside, with the myometrium in between and we choose the transvaginal route for performing the scan due to its proximity to the scar and better resolution. The mean scar thickness as measured by transvaginal sonography in the third trimester was 4.8 mm ± 1.6 which is slightly higher than their counterparts in previous studies. Of the 120 patient studied, 110 (91.7%) patients were posted for RECS while 10 (8.3%) had delivered by VBAC. The scar thickness in the third trimester had a significant relation with the mode of delivery using chi-squared test.Results: In this study, a receiver-operator characteristic (ROC) curve was constructed using the scar thickness in the third trimester and then determining the sensitivity and specificity with a range of cut-off. We concluded that a best cut-off value will be at 4.5 mm and this yielded a sensitivity of as 66.7%, specificity of 100%, positive predictive value of 100%, negative predictive value of 61.3% (by TVS ). These figures are quite acceptable and means that we can use this cut-off value in clinical diagnosis and management. Hence, transvaginal sonography is of a great value in prediction of uterine scar dehiscence on measuring the lower uterine segment thickness helping in proper selection of women for trial of VBAC. It is to be noted that further larger studies are still needed to confirm these results and to determine a definite cut-off value for scar thickness that the clinicians use in practical life.