Longitudinal Changes of Subpubic Arch Angle throughout Pregnancy.

OBJECTIVE: The objective of this study is to assess whether the subpubic arch angle (SPA) changes throughout pregnancy. MATERIALS AND METHODS: We recruited a group of nulliparous women in the first trimester of pregnancy. Each woman was assessed 3 times throughout pregnancy, once per each trimester, by measuring SPA using a recently described highly reproducible three-dimensional transperineal ultrasound (linear reconstruction with contrast enhancement technique; OmniView-volume contrast imaging). Repeated measures analysis of variance was used to study SPA changes during pregnancy. RESULTS: Overall, 97 women were included in the final analysis. SPA increased progressively and significantly (F = 27.824, p < 0.001) from the first to the second trimester (121.8 ± 8.7 vs. 123.5 ± 8.4°, p = 0.01) and from the second to the third trimester (123.5 ± 8.4 vs. 125.3 ± 8.1°, p = 0.01). CONCLUSION: SPA width increases progressively but slightly during pregnancy. Although this finding is interesting, the extremely small difference detected is unlikely to be clinically significant.

Narrow subpubic arch angle is associated with higher risk of persistent occiput posterior position at delivery.

OBJECTIVE: To determine whether the subpubic arch angle (SPA) measured by three-dimensional ultrasound is associated with the fetal occiput position at delivery and the mode of delivery. METHODS: Nulliparous women with an uncomplicated singleton pregnancy at ≥ 37 weeks' gestation were recruited from two tertiary centers between September 2013 and August 2015. All women underwent a three-dimensional transperineal ultrasound examination and the SPA was measured using the previously validated Oblique View Extended Imaging software. Data on the outcome of labor were obtained prospectively in all cases and the correlations between SPA and the fetal occiput position at delivery and the incidence of operative delivery were investigated. RESULTS: Overall, 368 women were included in the study. Fetal position at delivery was occiput anterior in 339 (92.1%) cases and occiput posterior (OP) in 29 (7.9%) cases. A significantly narrower SPA was found in the OP group compared with the occiput anterior group (104.4 ± 16.8° vs 116.4 ± 11.9°; P < 0.0001). The SPA was significantly narrower in women requiring obstetric intervention compared with in women with a spontaneous vaginal delivery. From multivariable logistic regression analysis, SPA and maternal height appeared to be significant predictors of both the fetal occiput position at delivery and the risk of operative delivery. The best cut-off value of SPA for predicting an OP position at delivery was 90.5°. CONCLUSION: A narrow SPA is associated with a higher risk of persistent OP position at delivery and of operative delivery. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Measurement of subpubic arch angle by three-dimensional transperineal ultrasound and impact on vaginal delivery.

OBJECTIVES: To assess whether antepartum measurement of the subpubic arch angle (SPAA) as a parameter of the bony pelvic outlet can predict vaginal delivery. METHODS: Between January 2007 and June 2011, 625 nulliparous women with a singleton pregnancy were recruited from the antenatal clinic to be interviewed and have a four-dimensional transperineal ultrasound examination. Ultrasound examinations were performed between 34 and 36 weeks of gestation. Volume ultrasound data were saved for offline analysis, blinded against all other data. The SPAA was measured in the axial plane and logistic regression analysis was used to examine the association between SPAA and outcomes of vaginal delivery vs Cesarean section in the second stage of labor, and normal vs assisted vaginal delivery. The association between SPAA and the duration of second stage of labor was also analyzed. RESULTS: Of the 625 women recruited initially, 14 ultrasound data files could not be retrieved, providing a total of 611 ultrasound images for measurement of SPAA. Complete obstetric and ultrasound data were obtained from 593 patients. Mean SPAA was 109.3° (range, 65.6-131.6°). There was no association between SPAA and the odds of a vaginal delivery (odds ratio, 1.01 (95% CI, 0.97-1.06)). However, there was evidence of an association between SPAA and duration of second stage of labor within the subgroup of women with a normal vaginal delivery (cause-specific hazard ratio, 1.02 (95% CI, 1.01-1.03); P = 0.003). CONCLUSIONS: SPAA is not useful for predicting vaginal delivery; however, there is an association between this parameter and the duration of the second stage of labor.

Predictive value of the trans-perineal three-dimensional ultrasound measurement of the pubic arch angle for vaginal delivery.

BACKGROUND: Numerous variables are linked to the success of vaginal delivery, including the subpubic arch angle (SPAA) during labor, the importance of which has not yet been fully elucidated. AIM: To examine the SPAA distributional characteristics and to ascertain SPAA's ability to predict the type and duration of labor. METHODS: We determined the SPAA and analyzed the corresponding data. We also evaluated the relationship between the SPAA and the mode of delivery and the duration of labor by regression. The present study comprised a total of 301 pregnant women who had given birth at Beijing Tiantan Hospital of the Capital Medical University between January and December of 2021. RESULTS: Our analysis of 301 pregnant women revealed that the SPAA measured using three-dimensional trans-perineal ultrasound had a minimum angle of 81° and a maximum angle of 122.2°. The angle in the normal vaginal delivery group was greater than that in the labor cesarean group (P = 0.000). The SPAA was a highly significant positive predictor of normal vaginal delivery (P = 0.000) with an area under the curve of 0.782 (P = 0.000; 95%CI: 0.717-0.848). We found the length of the second stage of labor to be positively influenced by the SPAA using linear regression analysis (P = 0.045). CONCLUSION: The SPAA was a highly significant positive predictor of normal vaginal delivery. The length of the second stage of labor and normal vaginal birth were predicted by SPAA.

Using transperineal ultrasound to predict labor onset.

BACKGROUND: Accurate diagnosis of labor onset is especially important for the counseling about elective induction of labor. The study aimed to evaluate whether transperineal ultrasound could better predict the timing and likelihood of spontaneous labor at term. METHODS: This single-center study was conducted between 2018 and 2019.Data on singleton pregnant women after 39 weeks and before labor onset were retrospectively reviewed. RESULTS: All the transperineal ultrasound parameters were well reproducible between the two doctors [intraclass correlation coefficient (ICC) for progression distance(PD) was 0.892, P<0.001], [ICC for angle of progression (AoP) was 0.881, P<0.001], [ICC for subpubic arch angle (SPA) was 0.766, P<0.001], [ICC for width of symphysis pubis (WSP) was 0.803, P<0.001]. For the pregnant women before 40 weeks, the width of symphysis pubis changed gradually with the of spontaneous labor (WSP) (r=0.33, P<0.05). For all included women, the SPA correlated with the time of spontaneous labor (SPA) (r=0.31, P<0.05). CONCLUSIONS: The antepartum transperineal ultrasound is a simple and objective technique that better observes the initiation of labor. And with the WSP and SPA we were able to predict labor onset and help in counseling about elective induction of labor.

Agreement between two 3D ultrasound techniques for the assessment of the subpubic arch angle.

OBJECTIVES: To assess the reliability of a new three-dimensional (3D) ultrasound technique for the measurement of the subpubic arch angle (SPA) and the agreement between two contrast-enhancing 3D ultrasound techniques. METHODS: We acquired two static 3D transperineal volumes from 72 nulliparous women using two ultrasound machines equipped with two different 3D contrast enhancement and linear reconstruction softwares: 1. Oblique View Extended Imaging with HD-Volume Imaging (OVIX-HDVI™), Samsung; 2. Omniview with Volume Contrast Imaging (Omniview-VCI™), GE Healthcare. An operator measured SPA once by OVIX-HDVI, and twice by Omniview-VCI, while another operator measured SPA once by Omniview-VCI. We evaluated intra- and inter-observer reproducibility of Omniview-VCI and intermethod agreement. Reproducibility and intermethod agreement were studied by means of intraclass correlation coefficient (ICC) and Bland-Altman method. RESULTS: Omniview-VCI SPA measurements showed excellent intraobserver and interobserver reproducibility (ICC 0.970; 95% C.I. 0.952 to 0.981, 0.932; 95% C.I. 0.893 to 0.957, respectively). Furthermore, Omniview VCI SPA measurements demonstrated excellent agreement with those performed by OVIX-HDVI technique (ICC 0.943; 95 C.I. 0.911 to 0.964). No systematic difference was found in any of the reliability studies. CONCLUSIONS: OmniView-VCI is a reliable method for SPA assessment. Both OmniView-VCI and OVIX-HDVI can be used interchangeably for SPA measurement.