Does Lower Uterine Segment Thickness Measurement Improve Birth Planning After Previous Cesarean Section?

Introduction Lower uterine segment (LUS) thickness measurement is frequently used to select patients for trial of labor after a previous cesarean section (TOLAC). To date no significant benefit of LUS measurement has ever been proven, and no standard protocol or clear cut-off value exists. The aim of this study was to evaluate the benefit of LUS measurement in a daily routine setting. Material and Methods In this retrospective study, we evaluated 631 pregnancies after previous cesarean section (CS). Ultrasound measurements of myometrial (mLUS) and/or full LUS (fLUS) thickness were performed in 399 (63 %) patients. The incidence, time, and mode of detection of uterine defects were studied. Sensitivity, specificity, positive (PPV) and negative predictive values (NPV) were calculated for different cut-off values of LUS thickness. Results Uterine defects were diagnosed in 28 (4.4 %) patients. Detection rate of ultrasound was low (13.6 %), with better sensitivity, specificity, PPV, and NPV at lower (2 mm (fLUS) / 1 mm mLUS): 75/96/48.3/98.7 %) than at higher cut-off values (3 mm (fLUS) / 2 mm (mLUS): 15.8/ 93.2/10.4/68.7 %). Discussion The benefit of LUS thickness measurement appears overestimated. As a large number of methodological factors trigger inaccuracy, a consistent protocol including both a transabdominal and a transvaginal scan performed by a trained examiner might improve accuracy. Exclusion of uterine defects might be more useful for prenatal selection after CS.