During the observation period, 457,825 deliveries were recorded. Among the 255,453 deliveries in women with a parity of greater than 1, 29,046 (11.37%) had a previous cesarean. The rate of choosing a trial of labor was 60.64% (Table 1). Within that trial-of-labor group, 15,154 women (86.04%) had spontaneous labor and 2459 (13.96%) required induction of labor. The success rate was 75.06% (11,374 of 15,154) for the spontaneous-labor group compared with 65.56% (1612 of 2459) for the induced-labor group. The average success rate was thus 73.73% (12,986 of 17,613).
When the previous-cesarean group was compared with the other deliveries (Table 2
), women with previous cesarean had a much greater frequency of placental disorders with subsequent bleeding, neonatal complications, and maternal problems such as febrile or thromboembolic complications. Only one woman died in the previous-cesarean group (of pulmonary embolism 11 days after an unsuccessful trial of labor with a subsequent repeat cesarean), compared with 14 women in the group without previous cesarean (no statistical significance).
Comparison between the trial-of-labor group and the elective repeat-cesarean group (Table 3) showed that maternal risks were consistently lower in the former, with the exception of uterine rupture. Perinatal death was, however, significantly higher for the trial-of-labor group (RR 1.74; 86 cases or 0.49%). A more detailed study of these infants revealed that 36 of them (41.86%) were less than 28 weeks of gestational age (compared with 18.75% in the group with primary repeat cesarean) and that several had malformations. Looking solely at the infants born after 28 weeks of gestational age without malformations in the previous-cesarean group, we found 43 cases of perinatal death: 10 in the primary repeat-cesarean group and 33 in the trial-of-labor group (RR 2.14; 95% CI 1.07, 4.27). This difference remained marginally statistically significant. Of these 43 cases of perinatal death, six were associated with uterine rupture (one in the elective repeat-cesarean group and five in the trial-of-labor group), nine were due to placental abruption (five occurred during labor and four before admission to the hospital, so that emergency repeat cesareans were performed), one was associated with placenta previa, three were linked to preeclampsia, 12 were caused by amniotic infection or premature rupture of membranes with or without preterm deliveries and respiratory distress syndrome, and 12 had differing reasons.
Table 4 shows that the following risk factors were statistically significant for an unsuccessful trial of labor: fetal malpresentation (RR 3.83; CI 3.53, 4.14), induced labor (RR 1.47; CI 1.37, 1.59), and fetal weight of 4000 g or greater (RR 1.45; CI 1.33, 1.58). The overall success rate in the group with fetal malpresentation was 42.31%; the subgroup with occipitoposterior presentation had a success rate of 57.96% and the subgroup with breech presentation had a success rate of 33.51%. The success rates after induced labor (65.56%) or with fetal weight of 4000 g and greater (65.93%) were still high. Combining the need to induce labor and fetal macrosomia of over 4000 g, however, led to a rate of only 57.02% for successful vaginal deliveries. In contrast, augmenting labor was not a risk factor for a failed trial of labor.
Uterine rupture was found in 0.32% (92 of 29,046 patients) of the previous-cesarean group, in 0.40% of the trial-of-labor group, and in 0.65% of the group after induction of labor. Analysis of the uterine-rupture group did not show a higher incidence of cephalopelvic disproportion (seven cases or 7.6% compared with 1696 or 5.9%; RR 1.30; CI 0.63, 2.67; P = .47) or of high birth weight (4000 g and above) (12 cases or 13.04% compared with 2888 or 9.97%; RR 1.31; CI 0.76, 2.24; P = .327). In contrast (Table 5), epidural anesthesia during labor was given more often in the group with uterine rupture (17 [24.29%] compared with 1480 [8.44%]; P rates of induced labor (RR 1.74; 17 [24.29%] compared with 13.92% in the nonrupture group; P = .013), but augmenting labor was not found to be a significant risk factor for uterine rupture (29 [41.43%] compared with 35.80% in the group without rupture; P = .327). Abnormal fetal heart rate tracing (23 [32.86%]; 3.85 times higher than in the group without rupture; P and failure to progress (15 [21.43%]; 2.69 times higher than in the group without rupture; P with uterine rupture.