The risk of failed induction and the possibility of uterine rupture are major concerns of clinicians caring for women undergoing a trial of labor after a previous cesarean delivery (TOLAC). The best method, efficacy, and safety of cervical ripening and/or labor induction in this population have not been established . Available evidence is inconclusive because no randomized trials have compared the outcome of induction of labor in women with prior cesareans with elective repeat cesarean delivery (ERCD); data are mostly limited to findings from retrospective studies of fair to poor quality . These data are insufficient for many reasons, including inconsistent definitions of uterine rupture and dehiscence, wide variation in induction protocols (eg, timing and dosage of prostaglandins and/or oxytocin administration), heterogeneity in patient populations, and inconsistency in primary outcome measures .
Cervical ripening and induction of labor in women attempting TOLAC will be reviewed here. Other issues relating to TOLAC are discussed separately. (See "Choosing the route of delivery after cesarean birth".)
LIKELIHOOD OF SUCCESSFUL INDUCTION
At least 50 percent of inductions in women with a prior cesarean delivery are successful, with the highest chance of success in women with a prior vaginal delivery and favorable cervix.
A 2005 systematic review identified 14 fair-quality studies, and no good-quality studies, on the benefits and risks of inducing labor in patients with prior cesarean delivery . Induction was more likely to result in cesarean delivery than spontaneous labor, consistent with findings from most studies of women without a scarred uterus (see "Induction of labor"). The mean vaginal delivery rates for women with a prior cesarean delivery undergoing spontaneous labor and oxytocin induction were 80 percent (range 65 to 89 percent) and 68 percent (range 56 to 82 percent), respectively. The risk of uterine rupture trended higher among women who were induced.
Subsequent to this review, a large prospective observational study including almost 12,000 women with one prior low transverse cesarean delivery compared pregnancy outcomes after induced versus spontaneous labor . As expected, induction of labor was associated with a significantly higher risk of unsuccessful trial of labor after a previous cesarean delivery (TOLAC) (ie, cesarean delivery) than spontaneous labor, but two factors significantly increased the chance of success: (1) a previous history of vaginal delivery; and (2) favorable cervical status (modified Bishop score ≥6). Successful induction occurred in 91 percent of women with a prior vaginal delivery and a favorable cervix, 77 percent of women with a prior vaginal delivery but an unfavorable cervix, 69 percent of women with no prior vaginal delivery but a favorable cervix, and 45 percent of women with no prior vaginal delivery and an unfavorable cervix.