Increase in cervical extensibility during labor induced after isolation of the cervix from the uterus in pregnant ewes.

Surgical transection of the cervix was done on eight ewes in late pregnancy. This procedure resulted in most of the length of the cervix being mechanically disconnected from the uterus. Labor was induced by injection of dexamethasone phosphate into a fetal hind limb during operation in four of the eight ewes. The success of the induction of labor was confirmed by observation of increased uterine activity and by measurement of the concentrations of progesterone and 17 beta-estradiol in peripheral plasma. Ewes were put to death approximately 48 hours after injection of dexamethasone and the extensibility of the isolated portion of the cervix was determined. Cervices taken from ewes in which labor had been induced were found to have softened considerably compared to control cervices taken from ewes in which the cervix had been transected without induction of labor. The results suggest that cervical softening can still occur during labor in the absence of any direct mechanical or local vascular connection between the cervix and uterus.