The cesarean birth rate has continued to climb despite efforts to counteract this trend. A major reason for this rise is the practice of doing an elective repeat cesarean. Our study used a statistical model of meta-analysis to analyze the findings of 29 individual studies that looked at the association between the success of a trial of labor and various preexisting conditions. We hypothesized that various preexisting factors, including cephalopelvic disproportion, previous breech, previous vaginal delivery, more than one previous cesarean, use of oxytocin, and the length of labor and extent of dilatation in the previous cesarean, would affect the prediction of the outcome of a trial of labor. After determining odds ratios for the individual preexisting factors from the individual studies, we calculated overall odds ratios which incorporated the findings from all of the studies. For previous cephalopelvic disproportion, the odds were 0.5 for a successful trial of labor; for prior breech, 2.1; for women with a previous vaginal delivery, 2.1; for women who had had more than one cesarean, 0.7; and for women receiving oxytocin, 0.3. We were unable to analyze other preexisting factors because the data were not available, but short discussions of some of these other factors are offered. Even though the success rates do vary with the different preexisting factors, the clinician may anticipate a greater than 50% chance for success in any individual labor.