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

Abstract

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.

Keywords: Bishop score; angle of progression; cervical length; induction of labor; posterior cervical angle; prediction; shear wave elastography.

Figure 1

The shear wave elastic measurements. The shear wave elastic measurements were made on the inner, middle and outer parts of the anterior (A) and posterior (B) cervical lip

Figure 2

The measurement of the posterior cervical angle, which is the inferior angle between the line joining the internal os and external os, and the line across the lower segment of the posterior uterine wall

Figure 3

The measurement of the angle of progression, which is the angle between a line crossing the longitudinal axis of pubic symphysis intersecting a line through its inferior point tangential to the outer edge of the fetal skull [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 4

The prediction of all cesarean deliveries. ROC curve for the prediction of all cesarean deliveries after induction of labor with AUC of 0.815 (95% CI 0.777‐0.85)

Figure 5

The prediction of cesarean section for failure to enter active phase. ROC curves compare the predictive ability of parity with ultrasonographic measurement (cervical length with inner cervical SWE, black line: AUC 0.888 (95% C: 0.853‐0.916) and parity with Bishop score (dashed line: AUC 0.819 (95% CI 0.778‐0.855) (P = 0.009). The diagnostic odds ratio is 17.41 (sensitivity of 82.5% and specificity of 78.7%) and 9.65 (sensitivity of 80% and specificity of 70.7%), respectively [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 6

The prediction of cesarean section for failure to enter active phase among nulliparous women. ROC curves compare the predictive ability of sonographic measurement (cervical length with inner cervical SWE (black line: AUC 0.816, 95% CI 0.759‐0.864) and Bishop score (dashed line: AUC 0.68, 95% CI 0.615‐0.74) (P = 0.0054). The diagnostic odds ratio is 12.34 (sensitivity of 70.0% and specificity of 84.1%) and 3.80 (sensitivity of 65.0% and specificity of 67.2%), respectively [Color figure can be viewed at http://wileyonlinelibrary.com]