OP25.06: Sonographic evaluation of the lower uterine segment in pregnant women with prior Caesarean section, a systematic review

To evaluate the accuracy of antenatal sonographical measurement of the the lower uterine segment (LUS) thickness in the prediction of the risk of uterine rupture during a trial of labor in women with a previous Caesarean section (CS). We performed an electronic search of Pubmed and EMBASE for relevant articles published between 1980 and 2011. We used the keywords pregnancy, lower uterine segment, Caesarean section, ultrasound and uterine defect to search PubMed and EMBASE. We included studies that reported on pregnant women with at least one previous CS that reported on the sonographic LUS appearance during pregnancy in relation to uterine defects observed during or immediately after delivery. Only studies that allowed construction of two-by-two tables comparing sonographic LUS appearance and the occurrence of uterine scar defect were included. A bivariate meta-regression model was used to calculate pooled estimates of sensitivity and specificity for risk score cut-off values. The incidence rates for uterine defects ranged from 0% to 3.7% and for uterine dehiscence from 1.5% to 25%. The vaginal birth after Caesarean rate ((number of VBAC / number of all women with a previous CS) × 100)) varied from 19% to 68% (median incidence 43%) and the vaginal birth after Caesarean success rate ((number of VBACs / number of women ondergoing a TOL) × 100)) from 20% to 78% (median incidence 64%). LUS thickness measurement using cutoffs between 1.4–2.5 mm reached a specificity of 89% (95% CI 75% to 96%) at a sensitivity of 85% (95% CI 60% to 95%). LUS thickness measurement using cutoffs between 2.5–3.5 mm reached a specificity of 91% (95% CI 75% to 0.97%) at a sensitivity of 71% (95% CI 32% to 92%). In this review, we found a good association between the thickness of LUS measured by ultrasound and the LUS thickness during delivery. Antenatal sonography is potentially effective in the prediction of the risk of uterine defect during labor.