Statistical analysis of shear wave speed in the uterine cervix

Although cervical softening is critical in pregnancy, there currently is no objective method for assessing the softness of the cervix. Shear wave speed (SWS) estimation is a noninvasive tool used to measure tissue mechanical properties such as stiffness. The goal of this study was to determine the spatial variability and assess the ability of SWS to classify ripened versus unripened tissue samples. Ex vivo human hysterectomy samples (n = 22) were collected; a subset (n = 13) were ripened. SWS estimates were made at 4 to 5 locations along the length of the canal on both anterior and posterior halves. A linear mixed model was used for a robust multivariate analysis. Receiver operating characteristic (ROC) analysis and the area under the ROC curve (AUC) were calculated to describe the utility of SWS to classify ripened versus unripened tissue samples. Results showed that all variables used in the linear mixed model were significant ( p < 0.05). Estimates at the mid location for the unripened group were 3.45 ± 0.95 m/s (anterior) and 3.56 ± 0.92 m/s (posterior), and 2.11 ± 0.45 m/s (anterior) and 2.68 ± 0.57 m/s (posterior) for the ripened ( p < 0.001). The AUCs were 0.91 and 0.84 for anterior and posterior, respectively, suggesting that SWS estimates may be useful for quantifying cervical softening.