[Studies on changes in the uterine cervix during pregnancy].

The uterine cervix becomes increasingly soft during pregnancy and at parturition in comparison with the non-pregnant state. The purpose of the study is to evaluate the changes in consistency of the cervix during pregnancy by two methods. One is based upon the acoustical theory that the elasticity of the tissue correlates to the sound velocity (V). V = (E/rho)1/2 where E is an elastic modulus and rho is the density of the tissue. The ultrasonic velocities of 355 pregnant and 12 non-pregnant women were measured and the data are as follows: Sound velocities were 1587.5 +/- 6.0m/sec in controls, 1579.8 +/- 6.1m/sec in the first trimester, and 1572.8 +/- 5.4m/sec in the third trimester. The other study involved the quantification of collagenous fibers of the tissue sections stained by Masson's trichrome stain in the cervical stroma by means of an image processing technique. Area ratios of collagenous fibers in cervical stroma were 68.6 +/- 20.2% in non-pregnant, 46.3 +/- 14.0% in the first trimester, and 29.1 +/- 10.3% in near term. Two conclusions were reached based on these studies. The gradual decline in sound velocity with the progress of gestation reflects the softening of the cervix. Automatic image-analysis of sections stained by trichrome stain showed a decrease in collagenous fibers during gestation. The above results suggest that a decrease in collagenous fibers may be involved in the process of the ripening of the cervix.