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

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.

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.

Sonographic risk assessment for an unplanned operative delivery: a prospective study

PURPOSE

To assess the value of pre-labor maternal and fetal sonographic variables to predict an unplanned operative delivery.

METHODS

In this prospective study, nulliparous women were recruited at 37.0-42.0 weeks of gestation. Sonographic measurements included estimated fetal weight, maternal pubic arch angle, and the angle of progression. We performed a descriptive and comparative analysis between two outcome groups: spontaneous vaginal delivery (SVD) and unplanned operative delivery (UOD) (vacuum-assisted, forceps-assisted and cesarean deliveries). Multivariate logistic regression with ROC analysis was used to create discriminatory models for UOD.

RESULTS

Among 234 patients in the study group, 175 had a spontaneous vaginal delivery and 59 an unplanned operative delivery. Maternal height and pubic arch angle (PAA) significantly correlated with UOD. Analysis of Maximum Likelihood Estimates revealed a multivariate model for the prediction of UOD, including the parameters of maternal age, maternal height, sonographic PAA, angle of progression (AOP), and estimated fetal weight, with an area under the curve of 0.7118.

CONCLUSION

Sonographic parameters representing maternal pelvic configuration (PAA) and maternal-fetal interface (AOP) improve the prediction ability of pre-labor models for a UOD. These data may aid the obstetrician in the counseling process before delivery.

Antepartum ultrasound prediction of failed vacuum-assisted operative delivery: a prospective cohort study

BACKGROUND

Failed vacuum-assisted delivery (VD) is associated with increased risk of maternal perineal trauma and neonatal morbidity. Knowledge of the risk factors related to failed VD is essential in the clinical decision-making.

OBJECTIVE

To elucidate the strength of association and the predictive accuracy of different ante-partum ultrasound parameters in predicting the risk of failed VD prior to the onset of Labor and to test the diagnostic performance of a multiparametric model including pregnancy and Labor characteristics, ante and intra-partum ultrasound in anticipating failed VD.

STUDY DESIGN

Prospective study of consecutive singleton pregnancies complicated by VD undergoing a dedicated ultrasound assessment at 36-38 weeks of gestation. Head circumference (HC), estimated fetal weight (EFW) and subpubic angle and (SPA) were recorded before the onset of Labor. At the time of the VD, occiput position, head perineum distance (HPD) and angle of progression (AOP) were also recorded. Multivariate logistic regression and area under the curve (AUC) analyses were used to explore the strength of association and test the diagnostic accuracy of different maternal, Labor and ultrasound characteristics in predicting g failed VD.

RESULTS

Four hundred eight pregnancies with successful and 26 with failed VD were included in the analysis. Fetuses experiencing failed VD had a larger HC (1.21 versus 1.07 MoM; p = .0001), a higher EFW z-value (0.56 versus 0.33 z values; p = .002) and a narrower SPA (114 versus 122 p = .0001) compared to those having a successful VD. At multivariable logistic regression analysis, maternal height (aOR 0.89 95% CI 0.76-0.98), nulliparity (aOR: 1.14 95% CI 1.06-1.36), HC MoM (aOR: 1.24 95% CI 1.13-1.55) and SPA angle (aOR: 0.82 95% CI 0.67-0.95), but not EFW (p = .08) were independently associated with failed VD. When intrapartum ultrasound variables were added to the multivariate model, fetal occipital position (aOR: 1.45 95th CI 1.11-1.99) and HPD (aOR: 0.77 95th CI 0.44-0.96) were independently associated with failed VD. A multiparametric model integrating pregnancy and Labor characteristics and ante-partum ultrasound variables had an AUC of 0.837 (95% CI 0.797-0.876) for the prediction of failed VE. The addition of intra-partum ultrasound variables to the prediction model, improved the accuracy for failed VD provided by maternal and antepartum ultrasound characteristics with an AUC of 0.913 (0.888-0.937).

CONCLUSION

Antepartum prediction of failed VD is feasible. HC, SPA but not EFW are independently associated and predictive of failed VD. Adding these variables to a multiparametric model including maternal and intrapartum ultrasound parameters improves the diagnostic accuracy for failed VD.

The usefulness of ultrasound before induction of labor

The indications for induction of labor have been consistently on the rise. These indications are mainly medical (maternal or fetal) or social or related to convenience or maternal preferences. With the increase in the prevalence of these indications, the incidence rates of induction of labor are expected to rise continuously. This poses a substantial workload and financial burden on maternity healthcare systems. Failure rates of induction of labor are relatively high, especially when considering the maternal, fetal, and neonatal risks associated with emergency cesarean deliveries in cases of failure. Therefore, it is essential for obstetricians to carefully select women who are eligible for induction of labor, particularly those with no clinical contraindication and who have a reasonable chance of ending up with a successful noncomplicated vaginal delivery. Ultrasound has an established role in the various areas of obstetrical care. It is available, accessible, easy to perform, and acceptable to the patient. In addition, the learning curve for skillful obstetrical ultrasound scanning is rather easy to fulfill. Ultrasound has always had an important role in the assessment of maternal and fetal well-being. Indeed, it has been extensively explored as a reliable, reproducible, and objective tool in the management of labor. In this review, we aimed to provide a comprehensive update on the different applications and uses of ultrasound before induction of labor for the prediction of its success and the potential improvement of its health-related maternal and fetal outcomes.

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.

Fetal head circumference and subpubic angle are independent risk factors for unplanned cesarean and operative delivery

INTRODUCTION

The aim of this study was to ascertain whether combined ultrasound assessment of fetal head circumference (HC) and maternal subpubic angle (SPA) prior to the onset of labor may predict the likelihood of an unplanned operative delivery (UOD) in nulliparous women at term.

MATERIAL AND METHODS

Prospective cohort study of singleton pregnancies in cephalic presentation. Pregnancies experiencing UOD secondary to fetal distress were excluded. HC was assessed transabdominally and SPA values were obtained from a reconstructed coronal plane on three-dimensional (3D) ultrasound performed translabially at 36-38 weeks of gestation. Maternal characteristics, HC expressed as multiple of median, and SPA were compared according to the mode of delivery. Logistic regression and receiver operating characteristics curve analyses were used to analyze the data.

RESULTS

597 pregnancies were included in the study. Spontaneous vaginal delivery occurred in 70.2% of the cases and UOD was required in 29.8%. There was no difference in pregnancy characteristics and birthweight between women who had a spontaneous vaginal birth compared with UOD. The HC multiple of median was larger (1.00 ± 0.02 vs. 1.03 ± 0.02, p ≤ 0.0001), whereas SPA was narrower in the UOD group (124.02 ± 13.64 vs. 102.61 ± 16.13, p ≤ 0.0001). At logistic regression, SPA (OR 0.91, 95% CI 0.89-0.93), HC multiple of median (OR 1.13, 95% CI 1.09-1.17) and maternal height (OR 0.95, 95% CI 0.92-0.99) were independently associated with UOD. When combined, the diagnostic accuracy of a predictive model integrating HC, SPA and maternal height was highly predictive of UOD with an area under the curve of 0.904 (95% CI 0.88-0.93).

CONCLUSIONS

Ultrasound assessment of fetal HC and maternal SPA after 36 weeks of gestation can identify a subset of women at higher risk of UOD during labor, for whom early planned delivery might be beneficial.

Transperineal sonographic assessment of angle of progression as a predictor of successful vaginal delivery following induction of labor

OBJECTIVES

To assess whether measurement of the angle of progression (AOP) before induction of labor (IOL) can predict successful vaginal delivery in nulliparous women.

METHODS

This was a prospective, observational study of nulliparous women with a singleton term pregnancy and an indication for IOL. Transperineal sonography was used to measure the AOP before cervical ripening. Since all women enrolled had a low Bishop score, 98.6% of them were induced with either intracervical extra-amniotic balloon catheter or vaginal prostaglandin E-2. The staff in the labor ward were blinded to the AOP measurements. Clinical data were retrieved from computerized medical records.

RESULTS

Of the 150 women included in the final analysis, 40 (26.7%) delivered by Cesarean section. The median AOP was narrower in women who had a Cesarean delivery than in those who delivered vaginally (90° (interquartile range (IQR), 84-94.5°) vs 98° (IQR, 90.8-105°); P < 0.001). When including only women who underwent Cesarean delivery for non-progression of labor (n = 27) in the analysis, an AOP of > 92° (derived from a receiver-operating characteristics curve) was associated with a successful vaginal delivery in 94.8% of women. Multivariate stepwise logistic regression analysis including maternal age, body mass index, gestational age, estimated fetal weight, fetal head station, indication for IOL and AOP demonstrated that only AOP was independently associated with the prediction of a successful induction.

CONCLUSION

AOP may be a useful sonographic parameter for predicting successful vaginal delivery among nulliparous women at term undergoing IOL; an AOP wider than 92° is associated with a high rate of vaginal delivery. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

A Geometric Capacity-Demand Analysis of Maternal Levator Muscle Stretch Required for Vaginal Delivery

Because levator ani (LA) muscle injuries occur in approximately 13% of all vaginal births, insights are needed to better prevent them. In Part I of this paper, we conducted an analysis of the bony and soft tissue factors contributing to the geometric "capacity" of the maternal pelvis and pelvic floor to deliver a fetal head without incurring stretch injury of the maternal soft tissue. In Part II, we quantified the range in demand, represented by the variation in fetal head size and shape, placed on the maternal pelvic floor. In Part III, we analyzed the capacity-to-demand geometric ratio, g, in order to determine whether a mother can deliver a head of given size without stretch injury. The results of a Part I sensitivity analysis showed that initial soft tissue loop length (SL) had the greatest effect on maternal capacity, followed by the length of the soft tissue loop above the inferior pubic rami at ultimate crowning, then subpubic arch angle (SPAA) and head size, and finally the levator origin separation distance. We found the more caudal origin of the puborectal portion of the levator muscle helps to protect it from the stretch injuries commonly observed in the pubovisceral portion. Part II fetal head molding index (MI) and fetal head size revealed fetal head circumference values ranging from 253 to 351 mm, which would increase up to 11 mm upon face presentation. The Part III capacity-demand analysis of g revealed that, based on geometry alone, the 10th percentile maternal capacity predicted injury for all head sizes, the 25th percentile maternal capacity could deliver half of all head sizes, while the 50th percentile maternal capacity could deliver a head of any size without injury. If ultrasound imaging could be operationalized to make measurements of ratio g, it might be used to usefully inform women on their level of risk for levator injury during vaginal birth.

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.

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.

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

Objective: To assess whether subpubic arch angle (SPA) measurement before labor onset can predict labor outcome among low-risk pregnant women. Methods: 3D ultrasound volume was transperineally acquired from a series of nulliparous women with uncomplicated pregnancy at term before the onset of labor. SPA was measured offline using Oblique View Extended Imaging (OVIX) on each volume performed by an investigator not involved in the clinical management. Labor outcome was prospectively investigated in the whole study group. Results: Overall, 145 women were enrolled in the study. Of these, 83 underwent spontaneous vaginal delivery, whereas obstetric intervention was performed in 62 cases (Cesarean section in 40 and vacuum extraction in 22). The SPA appeared to be significantly narrower in the women submitted to obstetric intervention compared with those undergoing spontaneous vaginal delivery (116.8 ± 10.3° vs. 123.7 ± 9.6°, p < 0.01). At multivariate analysis SPA and maternal age were identified as independent predictors of the mode of delivery. On the other hand, the duration of labor did not show a significant relationship with SPA. Conclusions: In low-risk nulliparous women at term gestation, SPA measurement obtained by 3D ultrasound before the onset of labor seems to predict the likelihood of an obstetric intervention but not the duration of labor.