Reliability of 3-Dimensional Transvaginal Sonographic Measurement of Lower Uterine Segment Thickness

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The purpose of this study was to report the intraobserver and interobserver reliability of transvaginal 3-dimensional (3D) sonographic measurement of lower uterine segment thickness. A prospective study of 60 pregnant women with previous low transverse cesarean deliveries was performed between 35 and 39 weeks' gestation. Two observers, blinded to the clinical data, independently measured the full lower uterine segment thickness by 2-dimensional (2D) transvaginal sonography. Three-dimensional volume data sets of the lower uterine segment were captured and analyzed more than 2 months later by both observers independently. Intraobserver, interobserver, and intermethod reliability was evaluated by median absolute differences, nonparametric limits of agreement, intraclass correlation coefficients (ICCs), and κ coefficients. The median full lower uterine segment thickness was 3.6 mm (range, 0.9-8.0 mm). Intraobserver reliability (median difference, 0.3 mm [interquartile range (IQR), 0.1-0.6 mm]; ICC, 0.88 [95% confidence interval (CI), 0.81-0.93]; κ, 0.87 [95% CI, 0.69-1.00]) and interobserver reliability (median difference, 0.3 mm [IQR, 0.1-0.5 mm]; ICC, 0.88 [95% CI, 0.81-0.93]; κ, 0.86 [95% CI, 0.66-1.00]) were excellent. Reliability between 3D and 2D sonography was moderate (median difference, 0.6 mm [IQR, 0.2-0.9 mm]; ICC, 0.78 [95% CI, 0.66-0.86]; κ, 0.56 [95% CI, 0.28-0.85]). However, intermethod reproducibility was improved when the full lower uterine segment thickness was less than 3.0 mm (median difference, 0.4 mm [IQR, 0.2-0.9 mm]). Full lower uterine segment thickness measured with 3D transvaginal sonographic data sets has excellent intraobserver and interobserver reliability. It also has good reproducibility with 2D sonography when the full lower uterine segment thickness is less than 3.0 mm.