Effect of third trimester formation of lower uterine segment on the thickness of previous cesarean scar measured by transvaginal sonography

Background Several studies have been conducted using various methods to evaluate the correlation of lower uterine segment (LUS) measurement with the risk of uterine rupture or dehiscence, with relative success. Patients and methods A cross-sectional study was conducted on 200 patients admitted for cesarean section. The patients were subjected to complete general, obstetric examination, and ultrasound measurement of LUS scar by transabdominal ultrasound (TAS) on partially full bladder and by transvaginal ultrasound (TVS) on empty bladder, and measurement of actual thickness intraoperatively. Results Uterine dehiscence was found in 24 (12%) cases. At 28 weeks, the mean scar thickness as measured by TAS was 6.796±1.84 mm, with a range of 3.6–11 mm, and by TVS was 4.11±1.29 mm, with a range of 3–10.1 mm, and at 38 weeks, the mean scar thickness as measured by TAS was 6.796±1.84 mm, with a range of 3.6–11 mm, and by TVS it was 2.9±0.9 mm, with a range of 1.3–3.9 mm. However, intraoperatively, it was 4.12±1.25 mm, with a range of 3–9 mm, by TVS. The cutoff value was 2.33 mm, and this yields a sensitivity of 96.2% and a specificity of 90%. Conclusion The LUS scar thickness measured sonographically is a good predictor of uterine scar dehiscence in pregnant women at term with previous cesarean section. Data from the present study demonstrated the superiority of TVS over TAS for the assessment of LUS scar thickness.