Changes in cervical compliance at parturition independent of uterine activity.

A new animal model has been developed to measure intrinsic changes of cerivcal compliance during spontaneous parturition or exposure to hormonal manipulation. Intermittent measurements of cervical compliance and continous measurements of uterine and cervical pressure were made during the last month of gestation of nine pregnant ewes. Cervical compliance increased abruptly and dramatically during spontanous and dexamethasone-induced parturition. Maternal progesterone supplementation at parturition inhibited uterine contractions but not the increase in cervical compliance, demonstrating the independence of the two events. The cervix was found to contract rhythmically and vigorously with a gradual decrease in activity as parturition approached.