Sonographic assessment of lower uterine segment thickness at term in women with previous cesarean delivery

The purpose of this study was to establish the validity of abdominal sonographic evaluation of lower uterine segment (LUS) thickness in full-term pregnancies with a single previous cesarean section, and to assess the usefulness of measuring LUS thickness in predicting the risk of uterine dehiscence.

Three hundred and thirty-six women with a single previous cesarean section who had an ultrasound measurement of the LUS thickness in pregnancy were enrolled. Abdominal sonographic assessment of LUS was carried out within 2 weeks of delivery. Sonographic measurements were correlated visual finding of a uterine scar at the time of the iterative cesarean section. Receiver operating curve analyses has been used to determine the detection rate and the risk of each actual value of LUS thickness vs. a thin uterine scar.

In our present study, 2.5 mm was considered the critical cut-off value of the LUS thickness. This critical cut-off value was derived from the ROC curve with sensitivity, specificity, PPV, and NPV of 90.9, 84, 71.4, and 95.5 %, respectively (using transabdominal ultrasound). The linear regression model analysis revealed that full LUS thickness of <2.5 mm was the only factor to be correlated with translucent lower uterine segment (C3) (8.8 vs. 0 %; P = 0.02).

Full LUS thickness of <2.5 mm is associated with a higher risk of uterine dehiscence.