For several decades the relative merits and risks of attempting a trial of labor after a previous cesarean delivery (TOLAC) have been debated. As cesarean delivery rates began to rise to very high levels in the United States, more people advocated the use of TOLAC. Small studies have suggested a significantly increased rate of uterine rupture among women undergoing TOLAC. Lydon-Rochelle and associates conducted a retrospective, population-based cohort analysis of data to assess the risks of uterine rupture and neonatal death with TOLAC.

The authors examined 20,095 women from a Washington State perinatal database who attempted vaginal delivery of a singleton fetus after previous cesarean delivery. Risk for uterine rupture was stratified according to TOLAC versus elective repeat cesarean delivery and by the use of prostaglandins or other means to induce labor. There were no significant differences in maternal age, race, or insurance status among the various groups.

Uterine rupture occurred in 0.16 percent of elective repeat cesarean deliveries without labor; 0.52 percent of patients selecting TOLAC with spontaneous onset of labor; 0.77 percent of patients in the labor induction group without prostaglandin use; and 2.45 percent of women whose labor was induced with prostaglandins. Neonatal death occurred in 6 percent of cases in which there was a uterine rupture, and a hysterectomy was necessary in 4 percent of these cases. The authors noted no difference in the increased rate of uterine rupture with prostaglandin induction in the study interval before and after 1996 (when use of misoprostol for induction of labor became widespread), implying that all prostaglandins were associated with increased risk.

The authors conclude that attempting vaginal delivery after a previous cesarean delivery is associated with an increased rate of uterine rupture, especially if labor is induced with prostaglandins.

editor's note: When interpreting the results of this study, it is important to differentiate between relative and absolute risk. In relative terms, the risk for uterine rupture is three times higher with TOLAC, and risk of neonatal death is 10 times higher if a uterine rupture occurs. In absolute terms, 99.5 percent of women who choose TOLAC without induction do not rupture, and neonatal death occurs in only 0.02 percent of cases. Weighing this rare but dreadful outcome against the common, but not catastrophic, increased maternal morbidity with routine cesarean delivery is prone to individual bias. Reasonable people will no doubt interpret the same data in different ways, but ultimately it is the expectant mother who must decide.—b.z.