A New Method to Measure the Subpubic Arch Angle Using 3-D Ultrasound.

Objectives: The aim of this study was to assess the reproducibility of both a new contrast-enhancing technique (Oblique View eXtended Imaging, OVIX; Samsung) and the recently reported 3-D multiplanar technique (MPT) in the measurement of the subpubic angle (SPA) among a group of women at term gestation. In addition, we aimed to study the intermethod agreement between the OVIX technique and MPT.

Methods: We acquired a transperineal 3-D ultrasound volume from 155 women with a singleton uncomplicated term pregnancy before the onset of labor. Each 3-D dataset was analyzed by the MPT and OVIX algorithm. The angle formed by the lower edges of the pubic rami (SPA) was measured twice by an operator and once by another operator for each technique in order to assess intra- and interobserver reproducibility. Reproducibility and intermethod agreement were studied by means of the intraclass correlation coefficient (ICC) and Bland-Altman method.

Results: SPA measurements performed with OVIX showed high intraobserver [ICC 0.912, 95% confidence interval (CI) 0.882-0.935] and good interobserver (ICC 0.791, 95% CI 0.724-0.844) agreement, while those measured with MPT showed moderate intraobserver (ICC 0.573, 95% CI 0.457-0.670) and good interobserver (ICC 0.640, 95% CI 0.537-0.724) agreement. Whereas the intermethod analysis showed good agreement between the MPT and the OVIX techniques (ICC 0.614, 95% CI 0.414-0.757), the SPA measured by MPT were significantly wider than those measured by OVIX (125 ± 12 vs. 120 ± 11°, p = 0.006).

Conclusions: OVIX is a reliable technique for SPA measurement. MPT overestimates the SPA in comparison with OVIX. Further studies are needed to assess its clinical utility.