Oxytocin use after previous cesarean: why a higher rate of failed labor trial?

When used for patients undergoing trial of labor after previous cesarean, oxytocin is associated with an increased failure rate. Previous reports have not studied why this occurs. From October 1984 to April 1986, 237 patients with previous cesareans underwent a trial of labor. The delivery outcomes of 73 women who received oxytocin were compared with those of the 164 who did not. Rates were similar for uterine scar dehiscence, uterine rupture, operative vaginal delivery, blood transfusions, endometritis, and low Apgar scores. Successful trial of labor occurred in 68% in the oxytocin group, compared with 89% in the no-oxytocin group. Failed trial of labor was significantly more frequent in patients who received oxytocin for induction of labor than in those who did not. When subjects who received oxytocin were divided into induction (N = 47) and augmentation (N = 26) groups, successful trial of labor occurred in 58% of the former group versus 88% of the latter group. Other characteristics of the augmentation group were spontaneous labor, greater cervical dilation and effacement at initiation of oxytocin, shorter duration of infusion, and lower oxytocin infusion rates. For patients who have had previous cesareans and who desire trial of labor, oxytocin by controlled infusion is safe. Successful trial of labor may be enhanced by awaiting spontaneous labor or inducing with a favorable cervix.