Sonoelastography as method for preliminary evaluation of uterine cervix to predict success of induction of labor

Ultrasonographic and elastographic evaluation of the canine cervix across oestrous cycle stages

This study evaluated B-mode ultrasonography and ultrasound elastography (UEl) for detecting structural and consistency changes in the canine cervix across the oestrous cycle, as the use of ultrasonographic techniques for this purpose remains underexplored. The present study aims to assess cervical features via ultrasound, acknowledging the critical role of the cervix in the canine oestrus cycle. Thirty-five bitches were evaluated during pro-oestrus, pre-ovulatory oestrus, peri-ovulatory oestrus, dioestrus and anoestrus. Progesterone levels, clinical signs, vaginoscopy and cytology were used to define the oestrous cycle phase. Cervical length, diameter, and the elastographic index (ElI) were measured, and the elastographic ratio (ElR) was calculated to compare cervical stiffness to the surrounding tissue. Cervical length and diameter values were observed to be higher during the pre-ovulatory and peri-ovulatory phases of oestrus (p < 0.05). ElI values in anoestrus were similar to dioestrus and significantly higher than pro-oestrus and pre-ovulatory oestrus (p < 0.05), reflecting greater cervical stiffness in anoestrus and dioestrus, while pro-oestrus and pre-ovulatory phases showed softer tissues. These findings underscore the utility of elastography in quantifying cervical tissue consistency and its correlation with hormonal influences, providing a novel diagnostic perspective for a more comprehensive understanding of reproductive health.

Strain ratio elastography of the uterine cervix and prediction of successful labor induction

BACKGROUND

Before labor induction, the uterine cervix is often evaluated by the Bishop score, or a modified Bishop score, to predict the duration and success of induction. However, more objective methods are wanted. Strain ratio elastography is a technique that evaluates the elastic modulus of a tissue. Using strain ratio elastography in combination with a reference material enables quantitative elastography of the uterine cervix.

OBJECTIVE

To evaluate the associations between the apparent elastic modulus of the cervical tissue assessed by strain ratio elastography and the cervical dilation time after labor induction.

METHODS

Twenty-two nulliparous pregnant women admitted for labor induction were included. A Bishop score, a cervical length measured by ultrasound and an elastic modulus evaluated by strain ratio elastography were obtained from all participants. Primary outcomes were cervical dilation time from labor induction to active labor and from active labor to full cervical dilation.

RESULTS

The strain ratio was not associated with the time from labor induction to active labor R2: 0,024 (P = 0.492), but there was a small association between strain ratio and time from active labor to full cervical dilatation R2: 0.180, however not significant (P = 0.063). The cervical length was associated with time from labor induction to active phase R2: 0.134 (P = 0.003), but not with time from active labor to full dilatation R2: 0.015 (P = 0.610).

CONCLUSIONS

The results indicate a possible importance of the elastic modulus for predicting time from active labor to full cervical dilatation, whereas the cervical length seems to be of greater importance for time from labor induction to active labor.

Recommendations for strain elastography of the uterine cervix

PURPOSE

Conventional vaginal strain ultrasound elastography, not based on shear-wave elastography imaging, can assess the biomechanical properties of the uterine cervix. This assessment may inform the risks of preterm birth and failed induction of labor. However, there is considerable variation in the approaches to strain elastography, including the placement of the region of interest (ROI). Therefore, our aim was to provide recommendations for cervical elastography.

METHODS

We conducted a literature review on (1) elastography principles, and (2) the cervical anatomy. Subsequently, we performed elastography scanning using a Voluson™ E10 Expert scanner with the BT18 software of (3) polyacrylamide hydrogel simulators, and (4) pregnant women.

RESULTS

Increasing the distance between the ROI and probe led to a decrease in the obtained strain value; a 53% decrease was observed at 17.5 mm. Similarly, an increased angle between the ROI and probe-centerline resulted in a 59% decrease for 40° angle. Interposition of soft tissue (e.g., cervical canal) between the ROI and the probe induced an artifact with values from the posterior lip being 54% lower than those from the anterior lip, even after adjusting for probe-ROI distance. Equipment and the recording conductance significantly influenced the results.

CONCLUSION

Our findings inform recommendations for future studies on strain cervical elastography.

Reliability of the sonographic evaluation for cervical length and elastography with pelvic parameters in term pregnancy by experienced operators with varying levels of experience

OBJECTIVE

To assess the reliability of sonographic measurements of six cervical and pelvic parameters by three sonographers with varying levels of experience.

METHODS

A cross-sectional study was conducted in pregnant women with a gestational age of ≥39 weeks. Each pregnant woman was examined by two sonographers with different levels of experience. Six parameters were measured: cervical length (CL), cervical strain elastography (extrinsic type), posterior cervical angle (PCA), fetal head-to-perineum distance (FHPD), fetal head-to-pubic symphysis distance (FHSD), and angle of progression (AOP). Intra- and interobserver reliabilities were assessed using the intraclass correlation coefficient with a 95% confidence interval. Pearson pairwise correlation coefficients were used to analyze the correlation between the parameter values.

RESULTS

In all, 66 pregnant women were enrolled in this study. We found excellent intraobserver reliability for measurements of CL, PCA, FHPD, FHSD, and AOP and good-to-excellent intraobserver reliability for cervical strain values in the cross-sectional view of the endocervix in the internal os area and cross-sectional view of the entire cervix in the internal os area. Interobserver reliability was excellent for all pelvic parameters, except for the FHPD. Strain values were moderate to excellent in the area of the internal os. A significant negative correlation between CL and strain values at the internal os was observed.

CONCLUSIONS

Pelvic parameters, except for FHPD, have excellent intra- and interobserver reliabilities. The high reproducibility of CL and cervical strain elastography at the internal os level, with a negative correlation between these two parameters, may play an important role in predicting successful induction of labor.

Predictive Value of Cervical Shear Wave Elastography in the Induction of Labor in Late-Term Pregnancy Nulliparous Women: Preliminary Results

The prediction of induction of labor continues to be a paradigm nowadays. Bishop Score is the traditional widely spread method but with a low reliability. Ultrasound cervical assessment has been proposed as an instrument of measurement. Shear wave elastography (SWE) should be a promising tool in the prediction of the success of labor induction in nulliparous late-term pregnancies. Ninety-two women with nulliparous late-term pregnancies who were going to be induced were included in the study. A shear wave measurement of the cervix divided into six regions (inner, middle and outer in both cervical lips), cervical length and fetal biometry was performed by blinded investigators prior to routine hand cervical assessment (Bishop Score (BS)) and induction of labor. The primary outcome was success of induction. Sixty-three women achieved labor. Nine women did not, and they underwent a cesarean section due to failure to induce labor. SWE was significantly higher in the inner part of the posterior cervix (p < 0.0001). SWE showed an area under the curve (AUC): 0.809 (0.677-0.941) in the inner posterior part. For CL, AUC was 0.816 (0.692-0.984). BS AUC was 0.467 (0.283-0.651). The ICC of inter-observer reproducibility was ≥0.83 in each region of interest (ROI). The cervix elastic gradient seems to be confirmed. The inner part of the posterior cervical lip is the most reliable region to predict induction of labor results in SWE terms. In addition, cervical length seems to be one of the most important procedures in the prediction of induction. Both methods combined could replace the Bishop Score.

Predictive value of cervical length by ultrasound and cervical strain elastography in labor induction at term

OBJECTIVE

This study aimed to examine whether addition of cervical elastographic parameters measured by ElastoScan for the cervix (E-cervix) improves the predictive value of cervical length (CL) in induction of labor at term by dinoprostone.

METHODS

We conducted a prospective, observational study between January 2020 and June 2020 in term primiparous women (n = 73) who were scheduled for labor induction by a 10-mg dinoprostone vaginal insert. The time intervals from the start of labor induction to regular uterine contractions and to vaginal delivery were calculated as the primary outcomes. We divided subjects into two groups using a threshold of 24 hours. Ultrasound measurements were compared between the two groups and the area under the curve (AUC) of the prediction model was calculated.

RESULTS

Women who delivered vaginally within 24 hours had a shorter CL and softer cervix than those who delivered after 24 hours. The combination of CL and elastographic parameters increased the AUC to 0.672 compared with CL alone (AUC = 0.637).

CONCLUSIONS

Measurement by E-cervix is relatively reproducible. Addition of cervical strain elastography slightly improves the predictive performance of CL in vaginal delivery within 24 hours. This technique is a promising ancillary tool for use with ultrasound.

ACR Appropriateness Criteria® Assessment of Gravid Cervix

Preterm birth remains the leading cause of perinatal morbidity and mortality. Although the greatest risk factor for preterm birth is a history of prior preterm birth, a short cervical length (≤25 mm) before 24 weeks' gestational age is also associated with increased risk of spontaneous preterm delivery. As such, cervical length assessment has become of particular interest in predicting those patients at risk for preterm birth. Other clinical scenarios (eg, preterm labor, induction of labor, and active labor) may arise, in which assessment of the cervix may be of interest. Ultrasound is the mainstay imaging modality for assessing the gravid cervix, with transvaginal ultrasound recommended in patients at high risk for preterm birth or suspected preterm labor. Transperineal ultrasound is an alternate approach in those cases where transvaginal ultrasound in contraindicated. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Quantitative ultrasound elastography and biometry of the bitch uterus in the early puerperium after vaginal delivery and caesarean section

Elastography is an actual imaging method used to qualitatively and quantitatively evaluate the elastic properties of tissues. The aim of this study was to evaluate and compare uterine tissue biometry and stiffness during post-partum period in brachycephalic bitches (n = 12) after c-section (GCS; n = 8) or normal delivery (GNB; n = 4). These animals were evaluated daily by abdominal ultrasound from the day of delivery until the 10th day post-partum; measuring uterine diameter, myometrial and endometrial thickness (mm) and shear wave velocity (SWV; m/s), by B-mode and ARFI (acoustic radiation force impulse) elastography, respectively. Uterine diameter was higher (p = .012) in animals submitted to c-section (15.26 ± 4.73 mm) than in normal birth (12.53 ± 2.64 mm) during the first 7 days post-partum. Uterine thickness gradually involuted in both groups (p < .0001), the myometrium during the first 9 days (p = .005) and the endometrium during the first 6 days (p = .003). The myometrial and endometrial SWVs were similar between types of delivery (p = .7846 and .8273) and presented a gradual increase (p = .411; .0043, respectively), during the first 10 days post-partum. It was concluded that bitches with normal delivery had smaller uterine thickness and faster puerperal involution than submitted to c-section, while uterine tissue stiffness was similar between delivery types and increased gradually during post-partum.

The predictive value of cervical shear wave elastography in the outcome of labor induction

Introduction

Bishop score, the traditional method to assess cervical condition, is not a promising predictive tool of the outcome of labor induction. As an objective assessment tool, many cervical ultrasound measurements have been proposed to represent the individual components of the Bishop score, but none of them can measure the cervical stiffness. Cervical shear wave elastography is a novel tool to assess the cervical stiffness quantitatively.

Material and methods

A total of 475 women who required labor induction were studied prospectively. Prior to routine digital assessment of the Bishop score, transvaginal sonographic measurement of cervical length, posterior cervical angle, angle of progression and shear wave elastography was performed. Shear wave elastography measurement was made at the inner, middle and outer regions of the cervix to assess homogeneity. Association of labor induction outcomes including the overall cesarean section and subgroups of cesarean section for failure to enter active phase, with cervical sonographic parameters and the Bishop score, were assessed using multivariate regression analyses. The predictive accuracy of the outcomes using models based on ultrasound measurement and the Bishop score was compared using the area under the receiver‐operating characteristics curves.

Results

Among 475 women, 82 (17.3%) required cesarean section. Shear wave elasticity was significantly higher in the inner cervical region than in other regions, indicating a greater stiffness (P < 0.001). Both inner cervical shear wave elasticity and cervical length were independent predictors of overall cesarean section (respective adjusted odds ratio [95% CI] 1.338 [1.001‐1.598] and 1.717 [1.077‐1.663]) and cesarean section for failure to enter active phase (respective adjusted odds ratio [95% CI] 1.689 [1.234‐2.311] and 2.556 [1.462‐4.467]), after adjusting for other covariates. Outcome prediction models using inner cervical shear wave elasticity and cervical length, had increased area under curve compared with models using the Bishop score (0.888 vs 0.819, P = 0.009).

Conclusions

The cervix is not a homogenous structure, with the inner cervix having the highest stiffness, which is an independent predictor of overall cesarean section, and specifically for those indicated because of failure to enter active phase. Models based on shear wave elastography and cervical length had higher predictive accuracy than models based on the Bishop score.

Addition of Cervical Elastography May Increase Preterm Delivery Prediction Performance in Pregnant Women with Short Cervix: a Prospective Study

BACKGROUND

We investigated whether there is a difference in elastographic parameters between pregnancies with and without spontaneous preterm delivery (sPTD) in women with a short cervix (≤ 25 mm), and examined the ability of elastographic parameters to predict sPTD in those women.

METHODS

E-Cervix^TM (WS80A; Samsung Medison, Seoul, Korea) elastography was used to examine the cervical strain. Elastographic parameters were compared between pregnancies with and without sPTD. Diagnostic performance of elastographic parameters to predict sPTD ≤ 37 weeks, both alone and in combination with other parameters, was compared with that of cervical length (CL) using area under receiver operating characteristic curve (AUC) analysis.

RESULTS

A total of 130 women were included. Median gestational age (GA) at examination was 24.4 weeks (interquartile range, 21.4-28.9), and the prevalence of sPTD was 20.0% (26/130). Both the elastographic parameters and CL did not show statistical difference between those with and without sPTD. However, when only patients with CL ≥ 1.5 cm (n = 110) were included in the analysis, there was a significant difference between two groups in elasticity contrast index (ECI) within 0.5/1.0/1.5 cm from the cervical canal (P < 0.05) which is one of elastographic parameters generated by E-Cervix. When AUC analysis was performed in women with CL ≥ 1.5 cm, the combination of parameters (CL + pre-pregnancy body mass index + GA at exam + ECI within 0.5/1.0/1.5 cm) showed a significantly higher AUC than CL alone (P < 0.05).

CONCLUSION

An addition of cervical elastography may improve the ability to predict sPTD in women with a short CL between 1.5 and 2.5 cm.

New techniques in evaluation of the cervix

The process of parturition is poorly understood, but the cervix clearly plays a key role. Because of this, recent research efforts have been directed at objective quantification of cervical remodeling. Investigation has focused on two basic areas: (1) quantification of tissue deformability and (2) presence, orientation, and/or concentration of microstructural components (e.g. collagen). Methods to quantify tissue deformability include strain elastography and shear wave elasticity imaging (SWEI). Methods to describe tissue microstructure include attenuation and backscatter. A single parameter is unlikely to describe the complexities of cervical remodeling, but combining related parameters should improve accuracy of cervical evaluation. This chapter reviews options for cervical tissue characterization.

Cervical elastography during pregnancy: clinical perspectives

Uterine cervix is a part of the uterus responsible for maintaining pregnancy till term. As long as the cervix remains long and firm and its internal orifice (os) is closed, it can withstand enlargement of the uterine contents and resultant growing pressure. Mechanical properties of the cervix change during pregnancy; the cervix ripens prior to delivery, then effaces and dilates with contractions of the uterus. Ripening of the cervix can be assessed using the Bishop score and ultrasonographically determined length of the cervical canal and internal os. Consistency is one of the cervical properties that change during the course of the maturation process. Until recently, cervical consistency has been assessed only manually, but in 2007, the first report on elastographic imaging of the cervix during pregnancy has been published. Elastography presents the ability of a tissue to deform under pressure. The softer the tissue, the easier it changes its shape. Different methods of elastography are used - static, when tissue displacement in response to manual compression or physiological movements of vessels is measured, or dynamic, when the speed of shear wave propagation is determined. Irrespective of the method, elastography provides information on the internal os stiffness; this parameter, impossible for manual assessment, was shown to correlate with pregnancy outcome and is a strong predictor of preterm delivery or successful labor induction. Although elastography seems to be a highly promising diagnostic option, still no consensus has been reached regarding an optimal method for uterine cervix assessment, and virtually all previous studies of various elastographic methods produced highly satisfactory results. Future studies need to identify the most promising and objective elastographic method which may serve as a novel tool for pregnancy management, preventing adverse events, such as preterm delivery and unsuccessful labor induction.

Elastographic measurement of the cervix during pregnancy: Current status and future challenges

The cervix is a cylindrical structure that is proximally connected to the uterus and distally to the vaginal cavity. The Bishop score has been used to evaluate the cervix during pregnancy. However, alternatives have been evaluated because the Bishop score is uncomfortable for patients, relies on a subjective examination, and lacks internal os data. Elastography has been used to assess the cervix, as it can estimate tissue stiffness. Recent articles on elastography for cervical assessment during pregnancy have focused on its usefulness for prediction of preterm birth and successful labor induction. There is a clinical need for cervical elastography, as an evaluation of biomechanical factors, because cervical length only assesses morphological changes. However, until now, cervical elastography has been studied in the limited field, and not shown a uniformed methodological technique. In this review, the current status, limitations, and future possibility of cervical elastography were discussed. Future studies should focus on overcoming the limitations of cervical elastography. Although the cervical elastography is presently an incompletely defined technique, it needs to be improved and evaluated as a method for use in combination with cervical length.

Definition of Failed Induction of Labor and Its Predictive Factors: Two Unsolved Issues of an Everyday Clinical Situation

OBJECTIVE

The objectives of this review were to identify the predictive factors of induction of labor (IOL) failure or success as well as to highlight the current heterogeneity regarding the definition and diagnosis of failed IOL.

MATERIALS AND METHODS

Only studies in which the main or secondary outcome was failed IOL, defined as not entering the active phase of labor after 24 h of prostaglandin administration ± 12 h of oxytocin infusion, were included in the review. The data collected were: study design, definition of failed IOL, induction method, IOL indications, failed IOL rate, cesarean section because of failed IOL and predictors of failed IOL.

RESULTS

The database search detected 507 publications. The main reason for exclusion was that the primary or secondary outcomes were not the predetermined definition of failed IOL (not achieving active phase of labor). Finally, 7 studies were eligible. The main predictive factors identified in the review were cervical status, evaluated by the Bishop score or cervical length.

DISCUSSION

Failed IOL should be defined as the inability to achieve the active phase of labor, considering that the definition of IOL is to enter the active phase of labor. A universal definition of failed IOL is an essential requisite to analyze and obtain solid results and conclusions on this issue. An important finding of this review is that only 7 of all the studies reviewed assessed achieving the active phase of labor as a primary or secondary IOL outcome. Another conclusion is that cervical status remains the most important predictor of IOL outcome, although the value of the parameters explored up to now is limited. To find or develop predictive tools to identify those women exposed to IOL who may not reach the active phase of labor is crucial to minimize the risks and costs associated with IOL failure while opening a great opportunity for investigation. Therefore, other predictive tools should be studied in order to improve IOL outcome in terms of health and economic burden.

Overview of the methods available for biomechanical testing of the uterine cervix in vivo

OBJECTIVE

To give an overview of the methods available for biomechanical testing of the non-pregnant and pregnant uterine cervix in vivo.

METHODS

The following databases were searched. PubMed, Embase, and Cochrane Library. Additional studies were identified from reference lists. Only studies on in vivo biomechanical testing on both pregnant and non-pregnant women were included.

MAIN OUTCOME MEASURES

Estimation of distensibility, compressibility, and biochemical composition of the uterine cervix.

RESULTS

The distensibility methods evaluated a physiologic variable and might serve as a gold standard; however, they may never be clinically useful as they involve instrumentation of the cervical canal. The compression methods evaluated an unphysiological variable but despite that, they seemed to evaluate biologically relevant figures and were non-invasive. Of the methods evaluating the biomechanical properties indirectly, those based on ultrasound may be clinically useful. Other indirect methods only measured variables within the most superficial layer of the distal uterine cervix, so further studies are needed to evaluate whether these measurements reflect the entire organ. Both compression methods and indirect methods were similar or superior to the Bishop score and to cervical length measurements regarding prediction of spontaneous preterm delivery and successful induction of labor in small studies.

CONCLUSION

The methods may have the potential to detect the biomechanical changes in the uterine cervix before the cervical length has shortened. The most promising methods need large-scale clinical testing regarding induction of labor and preterm delivery before they can be used in the clinic.