Supplementary Material for: 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.