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

Abstract

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.

Subpubic Arch Angle and Mode of Delivery in Low-Risk Nulliparous Women

“…However, since the reproducibility of this technique was not assessed, we suspect that 2D measurement of the SPA may not adequately reliable to promote the use of this approach in clinical practice. On the other hand, 3D ultrasound may provide clear images of the pubic bone on the coronal plane, and thanks to the OVIX algorithm, accurate and reproducible measurements of the SPA may be simply and quickly obtained as previously demonstrated by our group [4]. …”

“…In all eligible women included in the study group 3D volume was acquired by transperineal ultrasound (fig. 1) and the SPA was visualized and measured by means of Oblique View Extended Imaging (OVIX) as described elsewhere [4]. OVIX is a 3D ultrasound contrast enhancement technique with excellent reproducibility for the measurement of SPA [4] (fig.…”

“…The two examiners who carried out the SPA calculation were not involved in the clinical management of the patient during labor. Reproducibility of this measurement was assumed to be excellent as shown in a previous feasibility study [4]. …”

“…However, in that study the reproducibility of the SPA measurement by 2D ultrasound was not investigated, though this may represent a main limitation of the suggested technique. More recently, the use of 3D ultrasound was proved to be accurate and reproducible in measuring the SPA in early pregnancy and at term gestation [2,3,4]. However, very few data are present on the clinical utility of this 3D sonographic parameter [2].…”

Correlation between Subpubic Arch Angle and Mode of Delivery in Large-for-Gestational-Age Fetuses

“…Classic pelvimetry based upon clinical or radiological examination has been abandoned due to its low accuracy, reproducibility, and costeffectiveness [3]. Very recently, the use of ultrasound has proved to be reliable in assessing the subpubic arch angle (SPA) [11,12], whose size is related to the transverse diameter of the birth canal [13]. Some independent studies have shown that, in the general population, a narrow SPA at antepartum ultrasound is associated with prolonged labor [14][15][16] and an increased risk of obstetric intervention [17,18].…”