Mechanical properties of the ovine cervix during pregnancy, labour and immediately after parturition.

The stretch modulus (stress/strain) of strips of ovine cervical tissue in vitro was measured at different stages of gestation. A decrease in stretch modulus implies softening of the tissue. There was a gradual but progressive reduction in the stretch modulus with advancing pregnancy between 30 and 140 days gestation with a marked increase between 140 days gestation and the onset of labour (P less than 0.005). After the first trimester, the uterine end of the cervix was usually more distensible than the vaginal end. No further reduction in the stretch modulus of the cervix occurred between labour and delivery of the fetus. The results of this study suggest that while there is some softening of the ovine cervix during pregnancy, most of the softening takes place immediately prior to the onset of labour and delivery of the fetus.