Viscoelastic Behavior of the Rat Uterine Cervix at Mid-Pregnancy

Preterm labor is the leading cause of neonatal mortality and accounts for 70% of the total cost of neonatal health care. Premature softening of the cervix has been identified as one of the primary causes of preterm labor. As the biochemistry of the cervix is distinct between the proximal and distal portions, the objective of this study was to determine the viscoelastic properties of these portions in mid-pregnancy (Day 15–16) relative to virgin Long-Evans rats. This will serve to establish baseline data for future studies that will aim to induce preterm labor in this model. The cervix was divided into distal and proximal portions that were tested independently. Each portion was tested in unconfined compression to 20% strain and held for 4 minutes followed by a recovery period of 30 minutes. The stress-relaxation response was modeled using the quasi-linear viscoelastic (QLV) theory developed by Professor Fung (1972). The parameters governing the viscous response, C, τ₁ and τ₂, were found to be significantly different between virgin and pregnant tissues in distal portions; however τ₂ was the only viscous parameter found to be significantly different for the proximal portion (p<0.05). These results show an increased magnitude of the viscous response with more rapid relaxation for the pregnant cervix. Future studies will evaluate the cervix both postpartum and upon induction of preterm labor. Additionally, contractile and biochemical assays will be used to correlate these changes in passive behavior to active properties and tissue constituents.