A history of cesarean delivery implies a considerably elevated risk for a variety of peripartal complications for both mother and child, such as an increased frequency of extrauterine pregnancy,21 the necessity for hysterectomy, and febrile and thromboembolic complications.
Reports have described increased placental implantation disturbances (placenta previa, placental abruption) related to cesarean delivery21–24 (also Green R, Gardeil F, Turner MJ. Long-term implications of cesarean section [Letter]. Am J Obstet Gynecol 1997;176:254–5). Our data confirm these findings. We found a 2.06-fold elevated risk of vaginal bleeding with placenta previa during pregnancy in women who had a previous cesarean. We also confirmed an elevated risk of placental abruption in these women (during pregnancy, RR 1.87; during labor, RR 1.49).
Maternal death can occur from uterine rupture or placenta percreta after previous cesarean.24–26 According to the literature, uterine rupture occurred in approximately 0.5–0.8% of trials of labor (up to 1.5% when including bloodless dehiscence).4,11,27 In our trial-of-labor group, the risk of rupture was 0.40% (70 of 17,613), and in the primary repeat-cesarean group, it was 0.19% (22 of 11,433). This is a 42-fold higher risk for the previous-cesarean group compared with the group without previous cesarean (17 of 226,407, or 0.0075%). Uterine rupture during labor frequently manifests itself in fetal bradycardia or failure to progress.2,11 In our study, induction of labor raised the risk for uterine rupture from 0.40% to 0.65%. This ratio is still low, but we believe labor should be induced only if a clear indication is given. Epidural anesthesia was also associated with uterine rupture, but it remains unclear whether this is an independent risk factor because we could not perform a multivariate analysis.
Hillan28 demonstrated a marked increase in febrile morbidity after emergency cesarean. Our study revealed not only significantly elevated maternal risks (hysterectomy, thromboembolic complications, febrile morbidity, and maternal transfer to another hospital or another department) but also significantly elevated perinatal risks (5-minute Apgar score below 5, arterial pH below 7.00, neonatal transfer after birth, and perinatal death) after previous cesarean.
The frequency of trial of labor varies considerably among institutions (16.3–90%).9 Hueston and Rudy18 found that women undergoing a trial of labor were more likely to be younger, nonwhite, unmarried, living in households where all members were unemployed, and lacking private insurance. Our results confirm these findings concerning age, marital status, and insurance.
The overall success rate for vaginal birth was 73.73% (65.56% in the trial-of-labor group with induced labor and 75.06% in the trial-of-labor group without induced labor). The trial-of-labor group had fewer incidences of febrile morbidity and thromboembolic complications. However, perinatal mortality in infants older than 28 weeks’ gestation and without malformations was elevated: 0.19% compared with 0.09% in the elective repeat-cesarean group (RR 2.14; CI 1.07, 4.27; P = .031). Although this is marginally statistically significant, the absolute number is small and is in accordance with the generally slightly elevated risk for the infant during vaginal delivery compared with elective cesarean delivery. On the other hand, neonatal transfer was required less often. Uterine rupture occurred more often, but the necessity for peripartal hysterectomy did not, in contrast to the findings of McMahon et al.5 Thus, we conclude that a trial of labor is a safe procedure.
Weinstein et al17 found that a few factors can lead to a successful trial of labor, including the Bishop score, history of previous vaginal deliveries, and any of the following as the reason for previous cesarean: breech presentation, preeclampsia, multiple pregnancy, and placenta previa. McMahon et al5 found an increased rate of cesarean after a failed trial of labor when the maternal age was 35 years or older, the delivery took place at a community or regional hospital, the infant’s birth weight was greater than 4000 g, and the woman had no previous vaginal delivery. Learman et al12 studied 175 trials of labor and found that the risk factors for failure were induced labor and a high fetal station, but even these women had high rates of vaginal deliveries (67% and 75%, respectively). Only one subgroup, with both induced labor and large fetuses, had a 75% risk of cesarean delivery. We found similar results in our group of women who had induced labor, with a 65.56% success rate. In the group with the combination of fetal macrosomia and induced labor, we found a trial-of-labor success rate of 57.02%, which is not very encouraging. Thurnau et al20 studied a scoring system in which the fetal head and abdominal circumferences (by ultrasonographic measurement) were compared with the maternal pelvic inlet and midpelvic circumferences (by X-ray pelvimetry) and found that cesareans were likely if these measurements were unfavorable. Flamm and Geiger29 developed an admission scoring system. A trial of labor was more often successful when the patient was younger than 40 years (odds ratio [OR] 2.58), there was a history of vaginal birth (after first cesarean, OR 3.39; before first cesarean, OR 1.53; before and after first cesarean, OR 9.11), the reason for the first cesarean was other than failure to progress (OR 1.93), cervical effacement was present (more than 75%, OR 2.72; 25–75%, OR 1.79), and cervical dilatation was 4 cm or more upon admission to the hospital (OR 2.16).
A trial of labor should not be attempted when the patient has an unknown uterine scar type, a history of uterine rupture or scars in the upper segment of the uterus, absolute cephalopelvic disproportion, placenta previa, severe myopia complicated by retinal detachment, or fetal malpresentation incompatible with a safe vaginal delivery.17 The American College of Obstetricians and Gynecologists has published guidelines for these contraindications.1 In patients with a history of multiple cesareans, the risk for uterine rupture is even higher and has been associated with fetal death and serious neonatal disorders.4–6,11,24–27,30
One of the main problems seems to be the quick decision to perform the first cesarean. Consideration of cesarean should include not only the direct risks, but also the potential for late sequelae. Because our study was not randomized and our questionnaires did not ask why previous cesareans were performed, we cannot discuss the problem any further. We would like to point out that the overall frequency of cesareans in our working group was only 14% during the past 5 years (19,833 cesareans among 141,212 deliveries).
Our data show that a trial of labor after previous cesarean is safe and can be recommended in the majority of cases. Because the success rate for a trial of labor is only 57.02% when fetal macrosomia (greater than 4000 g) is combined with the need for inducing labor, we recommend an elective repeat cesarean in these situations. Although epidural anesthesia and induction of labor are associated with uterine rupture, we believe that a previous cesarean is not a strict contraindication for epidural anesthesia or induction of labor.