Ultrasound in labor: impact of a theoretical and practical course on caregiver's perspective and accuracy

Feasibility and reproducibility of new technique for measurement of transverse diameter of levator ani muscle hiatus using two-dimensional transperineal ultrasound in nulliparous women with term pregnancy

OBJECTIVES

The aim of the present study was two-fold. Firstly, we aimed to develop and describe a technique for measurement of the transverse diameter (TD) of the levator ani muscle (LAM) hiatus in the coronal view using two-dimensional (2D) transperineal ultrasound (TPUS) in nulliparous women with a term pregnancy. Secondly, we aimed to evaluate the feasibility and reproducibility of 2D-TPUS assessment of LAM hiatal TD and assess intermethod agreement between 2D-TPUS and three-dimensional (3D) TPUS measurement of TD in the axial plane, which is considered the gold standard in nulliparous women with term pregnancy.

METHODS

We recruited a group of nulliparous women with term pregnancy before the onset of labor. The study was conducted in two phases: Phase 1 involved developing and describing the 2D-TPUS technique for measuring LAM hiatal TD, and Phase 2 focused on assessing the technique's feasibility, reproducibility and intermethod agreement with 3D-TPUS measurement of LAM hiatal TD. In Phase 1, we enrolled 30 women. Each woman underwent acquisition of a 3D-TPUS volume, which was analyzed using multiplanar mode to identify and determine the appearance of the lateral borders of the LAM in the coronal plane, at the level of the plane of minimal hiatal dimensions. These borders were used as landmarks for TD measurement. Additionally, we measured the distance between the plane used for TD measurement and the center of the urethra in the axial view. In Phase 2, we recruited 100 women. Each woman underwent acquisition of three 2D-TPUS videoclips in the coronal plane, each encompassing a sweep of the entire LAM hiatus, and a 3D volume, all obtained during rest. On the 2D videoclips, TD was measured twice by one operator and once by another operator. In the 3D volume, TD was measured once, by one operator, in the axial plane; this measurement was considered the gold standard. Each operator was blinded to all other measurements during their assessments. We analyzed intraobserver and interobserver reproducibility and performed an intermethod (2D vs 3D) comparison. Bland-Altman analysis was conducted, and Levene's W0 test and Student's t-test were performed to explore clinical factors that might contribute to systematic differences.

RESULTS

In Phase 1, we identified successfully the landmarks denoting the lateral borders of the LAM hiatal TD in the coronal view. These appeared as two symmetrical hypoechogenic indentations located at the inner border of the hyperechogenic structure of the LAM, at the point of maximum distance between the two sides of the LAM. The distance between the urethra and the plane where TD should be measured using 3D-TPUS in the axial plane had a median of 4 mm and varied from 0 to 9 mm. This enabled us to describe a method for assessing LAM hiatal TD in the coronal plane using 2D-TPUS. In Phase 2, LAM hiatal TD was measured successfully in all 2D and 3D acquisitions from the entire group of 100 women. The analyses for intraobserver and interobserver reproducibility and the intermethod comparison (2D vs 3D) revealed almost perfect agreement in TD measurements using 2D-TPUS, with intraclass correlation coefficients of 0.95 (95% CI, 0.92-0.96), 0.87 (95% CI, 0.78-0.92) and 0.85 (95% CI, 0.78-0.90), respectively. The average differences between measurements were 0.1 mm for intraobserver, 1.0 mm for interobserver and 0.2 mm for intermethod repeatability. No systematic differences were observed in any of the measurement sets, except in the interobserver analysis, although this difference was clinically not significant (38.2 vs 37.2 mm, P = 0.01). None of the examined clinical factors (maternal body mass index and maternal age) exhibited a statistically significant impact on intraobserver, interobserver or intermethod reliability.

CONCLUSIONS

Utilizing our technique, described herein, to measure the LAM hiatal TD in the coronal view using 2D-TPUS is not only feasible but also highly reproducible and accurate in nulliparous women with term pregnancy. Moreover, it yields measurements that are comparable to those obtained in the reconstructed axial plane generated by 3D-TPUS. © 2024 International Society of Ultrasound in Obstetrics and Gynecology.

The correlation between levator ani co-activation and fetal head regression on maternal pushing at term

OBJECTIVE

To assess the correlation between fetal head regression and levator ani muscle (LAM) co-activation under Valsalva maneuver.

STUDY DESIGN

This study was a secondary analysis of a prospective cohort study on the association between the angle of progression (AoP) and labor outcome. We scanned a group of nulliparous women at term before the onset of labor at rest and under maximum Valsalva maneuver. In addition to the previously calculated AoP, in the present study, we measured the anteroposterior diameter of LAM hiatus (APD) on each ultrasound image. LAM co-activation was defined as APD at Valsalva less than that at rest, whereas fetal head regression was defined as AoP at Valsalva less than that at rest. We calculated the correlation between the two phenomena. Finally, we examined various labor outcomes according to the presence, absence, or co-existence of these two phenomena.

RESULTS

We included 469 women. A total of 129 (27.5%) women presented LAM co-activation while 50 (10.7%) showed head regression. Only 15 (3.2%) women showed simultaneous head regression and LAM co-activation. Women with coexisting LAM co-activation and head regression had the narrowest AoP at Valsalva in comparison with other study groups (p < .001). In addition, they had the highest risk of Cesarean delivery (40%) and longest first, second, and active second stage durations, although none of these reached statistical significance.

CONCLUSION

In nulliparous women at term before the onset of labor fetal head regression and LAM co-activation at Valsalva are two distinct phenomena that uncommonly coexist.

Uterine contraction frequency in the last hour of labor: how many contractions are too many?

OBJECTIVE

Increased frequency of uterine contractions is a component in the cluster of causal conditions that can lead to fetal hypoxia and acidosis and increase the risk for neonatal neurologic injury. For most international obstetrical societies, 5 contractions per 10 min averaged over 30 min is considered as the upper limit of normal uterine activity. We hypothesize that it might be safer to adopt an upper limit of 4 contractions per 10 min.

METHODS

We reviewed our 1970's research database containing 475 patients with closely monitored and well-documented labor and neonatal assessments that included cord blood (CB) pH, base excess (BE), and continuous recording of neonatal heart rate (NHR). Using data segregated by the proportion of the last hour before delivery when uterine contraction frequency (UCF) exceeded 4 and 5 contractions per 10 min respectively, we evaluated outcomes (CB BE, pH, Apgar scores at 1 min, the status of NHR at 16 min after birth, and the proportion of births that did not the result from normal spontaneous vaginal deliveries (NSVDs). ANOVA established relationships between UCF cutoffs and these outcomes. Our sample size is sufficiently large to provide the ability of UCF, per se, to accurately detect an alpha region of .05 88% of the time with an effect size of .15.

RESULTS

During the last hour prior to delivery, a UCF cutoff at 4 contractions per 10 min performed better than a UCF cutoff at 5 contractions per 10 min to enable the earlier identification of risks for abnormal outcomes. The longer UCF was increased, the worse were the outcomes that were measured, and the region >4 but ≤5 contractions identifies the beginnings of worsening conditions in a variety of measures of poor outcomes.

CONCLUSION

Lowering the recommended threshold for UCF from 5 to 4 contractions per 10-minute period as averaged over 30 min facilitates earlier detection of potentially compromised fetuses and is also an important contributor to a multicomponent contextualized approach to risk assessment.

Breech progression angle: new feasible and reliable transperineal ultrasound parameter for assessment of fetal breech descent in birth canal

OBJECTIVE

To assess the feasibility and reliability of transperineal ultrasound in the assessment of fetal breech descent in the birth canal, by measuring the breech progression angle (BPA).

METHODS

Women with a singleton pregnancy with the fetus in breech presentation between 34 and 41 weeks' gestation were recruited. Transperineal ultrasound images were acquired in the midsagittal view for each woman, twice by one operator and once by another. Each operator measured the BPA after anonymization of the transperineal ultrasound images. BPA was defined as the angle between a line running along the long axis of the pubic symphysis and another line extending from the most inferior portion of the pubic symphysis tangentially to the lowest recognizable fetal part in the maternal pelvis. Each operator was blinded to all other measurements performed for each woman. Intra- and interobserver reproducibility of BPA measurement was evaluated using the intraclass correlation coefficient (ICC). To investigate the presence of any bias, intra- and interobserver agreement was also analyzed using Bland-Altman analysis. Student's t-test and Levene's W₀ test were used to investigate whether a number of different clinical factors had an effect on systematic differences and homogeneity, respectively, between BPA measurements.

RESULTS

Overall, 44 women were included in the analysis. BPA was measured successfully by both operators on all images. Both intra- and interobserver agreement analyses showed excellent reproducibility in BPA measurement, with ICCs of 0.88 (95% CI, 0.80-0.93) and 0.83 (95% CI, 0.71-0.90), respectively. The mean difference between measurements was 0.4° (95% CI, -1.4 to 2.2°) for intraobserver repeatability and -0.4° (95% CI, -2.6 to 1.8°) for interobserver repeatability. The upper limits of agreement were 12.0° (95% CI, 8.9-15.1°) and 13.6° (95% CI, 9.9-17.3°) for intra- and interobserver repeatability, respectively. The lower limits of agreement were -11.2° (95% CI, -14.3 to -8.1°) and -14.4° (95% CI, -18.2 to -10.7°) for intra- and interobserver repeatability, respectively. No systematic difference between BPA measurements was found on either intra- or interobserver agreement analysis. None of the clinical factors examined (maternal body mass index, maternal age, gestational age at the ultrasound scan and parity) showed a statistically significant effect on intra- or interobserver reliability.

CONCLUSIONS

BPA represents a new feasible and highly reproducible measurement for the evaluation of fetal breech descent in the birth canal. Future studies assessing its usefulness in the prediction of successful external cephalic version and breech vaginal delivery are needed. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Transperineal ultrasound assessment of maternal pelvic floor at term and fetal head engagement

OBJECTIVES

To evaluate the association between pelvic floor dimensions in nulliparous women at term and fetal head engagement, as assessed by transperineal ultrasound.

METHODS

This was a prospective observational study of nulliparous women at term. Before the onset of labor, transperineal ultrasound was used to measure the anteroposterior diameter (APD) of the levator hiatus and the angle of progression (AoP) at rest, on maximum pelvic floor muscle contraction and on maximum Valsalva maneuver (before and after visual feedback). We assessed the correlation between pelvic floor static and dynamic dimensions (levator hiatal APD and levator ani muscle coactivation) and AoP, which is an objective index of fetal head engagement.

RESULTS

In total, 282 women were included in the analysis. Among these, 211 (74.8%) women had a vaginal delivery while 71 (25.2%) had a Cesarean delivery. AoP was narrower in the Cesarean-delivery group at rest, on maximum pelvic floor muscle contraction and on maximum Valsalva, whereas no differences in levator hiatal APD were found between the two groups. We found a negative correlation between levator hiatal APD at rest, on maximum pelvic floor muscle contraction and on maximum Valsalva and the duration of the second stage of labor. There was a positive correlation between AoP and levator hiatal APD on maximum Valsalva maneuver after visual feedback (r = 0.15, P = 0.01). Women with levator ani muscle contraction on Valsalva maneuver (i.e. coactivation), both pre and post visual feedback, had a narrower AoP at rest and on maximum Valsalva. After visual feedback, women with levator ani muscle coactivation had a longer second stage of labor than did those without (80.8 ± 61.4 min vs 62.9 ± 43.4 min (P = 0.04)).

CONCLUSIONS

Smaller pelvic floor dimensions and levator ani muscle coactivation are associated with higher fetal head station and with a longer second stage of labor in nulliparous women at term. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.

Feasibility, Reliability, and Agreement of Transperineal Ultrasound Measurement: Results from a Longitudinal Cohort Study

OBJECTIVES

To evaluate the feasibility, reliability, and agreement of serial transperineal ultrasound (TPU) assessment of fetal head station (parasagittal angle of progression [psAOP], head-perineum distance [HPD], and head-symphysis distance [HSD]) and sonographic cervical dilatation (SCD), compared to fetal head station and cervical dilatation determined by vaginal examination, respectively.

METHODS

This was a prospective longitudinal study in singleton pregnancies undergoing induction of labor at term. Paired assessment of fetal head station and cervical dilatation by vaginal examination, with TPU assessment of psAOP, HPD, HSD, and SCD was made serially. Feasibility, correlation, reliability, and agreement were determined.

RESULTS

1,139 paired measurements among 326 women were included. psAOP and HPD were achievable in all assessments. HSD was not achievable in 3.4% (11/326) due to high fetal head station. Fetal head station by vaginal examination was positively correlated with psAOP (rho = 0.70) but negatively correlated with HPD (rho = -0.57) and HSD (rho = -0.52). The feasibility to measure SCD reduced as cervical dilatation increased. Cervical dilatation and SCD were positively correlated (rho = 0.96) with strong agreement (concordant correlation coefficient = 0.925).

CONCLUSIONS

Measurements of psAOP and HPD are feasible and correlate significantly with fetal head station by vaginal examination. Measurement of HSD is not feasible when fetal head station is high. Measurement of SCD is feasible, but it is more difficult in the advanced stage of labor. The correlation, reliability, and agreement between SCD and cervical dilatation by vaginal examination are high.