[An objective measurement of softening of uterine cervix using tactile sensor for hardness]

The authors studied an objective measurement for cervical softening by means of a tactile sensor equipped with a piezoelectric swing element made from ceramic. The hardness of objects was indicated by changes in frequency (delta f) measured by this sensor. The authors measured the hardness of cervixes in 66 (non pregnant, pregnant, delivering and postpartum) Sprague-Dawley rats with the sensor. After the measurement of delta f, the rats' cervixes were removed, and the ratios of their dry weight to wet weight (weight-ratio) and hydroxyproline contents were measured. The delta f of rats' cervixes increased during pregnancy and became maximum at delivery. The weight-ratio also increased and correlated with delta f (r = 0.812). The hydroxyproline content decreased during pregnancy and correlated with delta f (r = 0.674). The hardness of the cervixes of 26 non pregnant and 192 pregnant women and their Bishop scores were also measured. The delta f of pregnant women's cervixes increased significantly in comparison with those of non pregnant women. The delta f of cervixes in primiparas correlated with the progress of pregnancy (r = 0.408). A moderate correlation between the delta f of cervixes and Bishop scores was also observed in the pregnant women. These results show that the tactile sensor may be able to be used in the objective measurement of hardness of the uterine cervix.