Characterization of viscoelastic behavior of rat cervix in the last trimester of pregnancy

Quantitative measurement of mechanical properties of cervix is an effective tool to diagnose cervical insufficiency, specifically in the last trimester of pregnancy when preterm birth is mostly probable to occur. The objective of this study was to characterize the viscoelastic behavior of rat cervix at different displacement levels and rates early in the last trimester of pregnancy. Distinct displacement levels and rates were employed to measure the tensile and load-relaxation properties of cervices from 16 days postconception pregnant rats. After preconditioning, 2 millimeters uniaxial displacement was applied to the distal halves of five rat’s cervices circumferentially at displacement rates of 0.01, 0.1 and 1 mm/sec. This displacement was held for 10 minutes while the tissues were mostly relaxed. The same procedure was repeated for the displacement levels of 1, 1.5 and 2 millimeters at the rate of 1 mm/sec. Tensile and loadrelaxation curves were well described by a quasi-linear viscoelastic model. Statistical analysis revealed significant correlation between the change in displacement levels and rates, and the elastic response of the tissues. The viscous response, though, did not show strong dependency on displacement levels as well as displacement rates. Cervix becomes considerably stiffer and exhibits less viscous effects in increasing rates. However, higher displacement levels result in lower strength of the tissue. These results show the viscoelastic behavior of cervix in the last trimester of pregnancy. These mechanical characterizations may be useful for prediction of cervical insufficiency and preterm birth.