Transabdominal and Transvaginal Ultrasonographic Assessment of Lower Uterine Segment Thickness in Pregnant Women Before Repeat Cesarean Section

INTRODUCTION: The selection of repeat cesarean delivery instead of trial of labor after cesarean (TOLAC) has a great contribution to cesarean rate. Ultrasonographic measurement of lower uterine segment (LUS) thickness for prediction of real uterine thickness was investigated by several researchers. In this study, LUS transvaginal (TV) and transabdominal (TA) ultrasonography (USG) measurements were evaluated for usefulness in patients with the previous cesarean scar.
METHODS: Pregnant patients between 37 and 40 weeks of gestational age who were admitted to our clinic with the decision of repeat cesarean delivery were evaluated by TV and TA USG by measuring the LUS full-thickness and myometrium before cesarean delivery. The patients were divided into two groups: Translucent LUS and intact myometrium. The real myometrial thickness also assessed by vernier caliper in the operation. Correlations between ultrasonographic and vernier caliper measurements were analyzed and cutoff values for the ultrasonographic measurements of LUS were evaluated.
RESULTS: Manual caliper measurements had a correlation (r) of 0.347 with TA USG full thickness, 0.337 with myometrial measurements, 0.443 with TV USG full thickness, and 0.475 with myometrial measurements. The extremely thin LUS ratio was 7.07% (n=14). Receiver operating curve, cutoff values are 3.55 mm for TA USG full-thickness LUS measurements, 2.75 mm for TV USG full-thickness, and 1.35 mm for TV USG myometrial LUS measurements.
DISCUSSION AND CONCLUSION: LUS USG measurements are useful for predicting the intact LUS and can be used in clinical decision-making for TOLAC, but the low positive predictive value suggests that it cannot be recommended in the prediction of extremely thin LUS.