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Sonographic Evaluation of the Lower Uterine Segment in Patients With Previous Cesarean Delivery

Department of Obstetrics and Gynecology, North York General Hospital, Toronto, Ontario, Canada (V.Y.T.C.); and BSA Diagnostic Imaging, Toronto, Ontario, Canada (O.C.C., B.S.A.).

Address correspondence and reprint requests to Vincent Y. T. Cheung, MBBS, FRCOG, FRCSC, RDMS, Department of Obstetrics and Gynecology, North York General Hospital, 4001 Leslie St, Toronto, Ontario M2K 1E1, Canada. E-mail: vcheung{at}nygh.on.ca.

Objective. To evaluate the appearance of the lower uterine segment (LUS) in pregnant women with previous cesarean delivery and to compare the LUS thickness with that in women with unscarred uteri. Methods. In a prospective study, sonographic examination was performed on 53 pregnant women with previous cesarean delivery (cesarean group), 40 nulliparas (nullip-control), and 40 women who had 1 or more childbirths with unscarred uteri (multip-control) between 36 and 38 weeks’ gestation to assess the appearance and compare the thickness of the LUS. In the cesarean group, the sonographic findings were correlated with the delivery outcome and the intraoperative LUS appearance. Results. In the cesarean group, 44 patients (83.0%) had a normal-appearing LUS indistinguishable from that of control groups; 2 patients (3.8%) had an LUS defect suggestive of dehiscence; and 7 patients (13.2%) had thickened areas of increased echogenicity with or without myometrial thinning. Although the cesarean group had a thinner LUS (1.9 ± 1.4 mm) when compared with both the nullip-control group (2.3 ± 1.1 mm; P > .05) and the multip-control group (3.4 ± 2.2 mm; P < .001), only the latter difference achieved statistical significance. One of the 2 patients who had a sonographically suspected LUS defect had confirmed uterine dehiscence during surgery. An intraoperatively diagnosed paper-thin LUS, when compared with an LUS of normal thickness, had significantly smaller sonographic LUS measurements (1.1 ± 0.6 versus 2.0 ± 0.8 mm, respectively; P = .004). Conclusions. Prior cesarean delivery is associated with a sonographically thinner LUS when compared with those with prior vaginal delivery. Prenatal sonographic examination is potentially capable of diagnosing a uterine defect and determining the degree of LUS thinning in patients with previous cesarean delivery.

Key Words: cesarean delivery • lower uterine segment thickness • previous cesarean delivery • sonography • uterine rupture • vaginal birth after cesarean delivery

Abbreviations: LUS, lower uterine segment • VBAC, vaginal birth after previous cesarean delivery

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