Uterine rupture is one of the most feared obstetric complications, carrying an increased risk of maternal and perinatal morbidity and mortality.1 In the developed world, the incidence of uterine rupture is less than one per 1000 deliveries, the majority of which occur in women with a previous cesarean delivery.1 Twenty years ago, a woman in North America with a previous cesarean delivery was almost exclusively offered repeat cesarean delivery because of the concern of uterine rupture in a subsequent labor. However, in the early 1980s, national consensus opinions in Canada and the United States encouraged both obstetricians and pregnant women to consider a trial of labor for vaginal delivery after one previous low transverse cesarean delivery.2,3 The advantage of successful vaginal birth after previous cesarean delivery (VBAC) is reduced maternal morbidity compared with repeat elective cesarean.4 Successful introduction of this policy was followed by widening the indications for labor to include induction and augmentation of labor,5–8 and, in selected cases, women with more than one previous low transverse cesarean.9,10 As the practice of VBAC was increasingly embraced in North America in the late 1980s and 1990s, a number of reports suggested a more cautious approach, particularly with regard to cervical ripening, induction, and augmentation of labor.11–14 The most consistent and serious risk, albeit rare, involved uterine rupture with perinatal morbidity and mortality.4 A recent statement by the American College of Obstetricians and Gynecologists has urged a more rigorous selection of patients and facilities for VBAC.15
We, therefore, undertook a population-based study of uterine rupture in one Canadian province for the 10-year period 1988–1997 to establish the incidence of uterine rupture, the relationship to VBAC, and the maternal and perinatal implications of complete versus incomplete rupture. During this time, a policy of VBAC was encouraged in obstetric units throughout the province.
MATERIALS AND METHODS
The Atlee Perinatal Database, which codes all deliveries greater than 500 g occurring in hospitals in Nova Scotia, was used to identify all cases of uterine rupture within the province from 1988 to 1997. The Nova Scotia Atlee Perinatal Database is abstracted by trained health records personnel from standardized clinical forms and hospital medical records across the province of Nova Scotia. The database is subjected to data quality assurance with periodic abstraction studies. The province of Nova Scotia has a population of approximately one million with about 12,000 deliveries annually. All women were delivered in hospitals by obstetricians or family physicians in consultation with an obstetrician. The charts of patients with uterine rupture were verified and reviewed for the past obstetric and gynecologic history, gestational age, onset of labor, diagnosis of rupture, type of rupture, and maternal and perinatal outcome. Labor was classified as: no labor, spontaneous, induction, and augmentation. Induction of labor was further subdivided into amniotomy, oxytocin, or prostaglandin. The diagnosis of uterine rupture was by: abnormal fetal heart rate, vaginal bleeding, pain, or at laparotomy. The type of uterine rupture was classified as complete if all layers of the uterine wall were separated and incomplete (dehiscence) if the uterine muscle was separated but the visceral peritoneum was intact. Maternal complications were sought as follows: death, laparotomy, hysterectomy, blood transfusion, regional or general anesthesia, and intensive care. Perinatal complications included intrapartum death, neonatal death (28 days), 5-minute Apgar score less than 7, asphyxia, needing ventilation for more than 1 minute, postasphyctic convulsions, increased intracranial pressure and brain necrosis, grade 3 or 4 intraventricular hemorrhage, and intensive care. Asphyxia was defined as moderate if the infant was blue and required intermittent positive pressure ventilation for up to 1 minute, and severe if the neonate was pale at birth and needed continuous intermittent positive pressure ventilation.
The χ2 and Fisher exact tests, where required, were used to compare categoric variables. P values of < .05 were considered statistically significant, and 95% confidence intervals were calculated where appropriate. Epi-Info 6.04 was used for statistical analysis (Centers for Disease Control and Prevention, Atlanta, GA).
During the 10 years 1988–1997 there were 114,933 deliveries, of which 11,585 (10%) were to women who had a previous cesarean delivery. Of those with a previous cesarean delivery, 4516 (39%) opted to attempt VBAC, and of these, 3624 (80%) achieved vaginal delivery, giving a VBAC rate of 31%. There were 39 cases of uterine rupture (18 complete, 21 dehiscence), and of these, 36 of 39 (92%) were in women with a previous cesarean delivery. The demographic characteristics of those with complete rupture and dehiscence are compared in Table 1. Three of the 39 (8%) uterine ruptures, all complete, occurred in the unscarred uterus: two women (gravida 2, para 0, aborta 1; gravida 4, para 2, aborta 1) had a previous dilation and curettage after spontaneous miscarriage, and one woman (gravida 1, para 0) had no previous surgery. The incidence of complete rupture and dehiscence in the total population, those with previous cesarean delivery, and those attempting VBAC are shown in Table 2. Of the 36 ruptures in women with a previous cesarean delivery, 33 had a low transverse incision (12 complete, 21 dehiscence), and three, all complete ruptures, had a vertical incision (two classic, one low vertical).
The characteristics of labor in the women with uterine rupture are shown in Table 3. Ten women (four complete, six dehiscence) had no labor: four had two previous low transverse cesareans, one low transverse, two classic, one low vertical, and one no scar. Of the 14 women with complete rupture who had labor, six of 14 (42.9%) received an oxytocic drug for induction (oxytocin or vaginal prostaglandin E2) or augmentation of labor (oxytocin), and six of 15 (40%) of the dehiscence group who labored received an oxytocic drug for induction of labor.
The diagnosis of uterine rupture was most commonly made by an abnormal fetal heart rate, with or without concomitant pain and vaginal bleeding. Of those women who underwent labor, eight of 14 (57%) of complete and six of 15 (40%) of dehiscence were diagnosed by abnormal fetal heart rate. The remaining nine complete ruptures were diagnosed primarily by pain ± vaginal bleeding. Four of the 21 dehiscence were diagnosed by pain ± vaginal bleeding, and 11 (52.4%) of all dehiscence were asymptomatic and discovered only at the time of repeat cesarean delivery—either elective or in labor.
There were no maternal deaths. The maternal morbidity is listed in Table 4 and shows a significantly higher rate of blood transfusion (odds ratio 7.60, 95% confidence interval 1.14, 82.14, P = .025) and emergency general anesthesia (odds ratio 5.03, 95% confidence interval 1.06, 25.30, P = .018) in those patients with complete uterine rupture. All women had laparotomy, and two bled after vaginal delivery, leading to uterine exploration and the diagnosis of complete rupture.
The perinatal outcome is shown in Table 5. The only stillbirth occurred in a para 2 woman, without a uterine scar but with a previous dilation and curettage for miscarriage, in whom complete uterine rupture occurred after spontaneous onset of labor at term. There were three neonatal deaths, all in women with a previous cesarean delivery. Two of these were caused by lethal anomalies known before labor. One was secondary to severe asphyxia in a woman with one previous low segment cesarean delivery in spontaneous labor at term. A nonreassuring fetal heart pattern and vaginal bleeding prompted cesarean delivery, which confirmed complete rupture of the cesarean scar. The infant was born severely asphyxiated (Apgar scores 1 and 3 at 1 and 5 minutes, respectively), resuscitated, and transferred to a tertiary neonatal unit where he died 12 days later. There were no other neonates with intraventricular hemorrhage, postasphyctic convulsions, increased intracranial pressure, or brain necrosis. As shown in Table 5, compared with uterine dehiscence, those infants (excluding lethal anomalies) born after complete uterine rupture had significantly higher rates of severe asphyxia (P < .01), 5-minute Apgar score less than 7 (P < .001), and intensive care (P = .04).
In developed countries, the majority of cases of uterine rupture occur in women who have previously undergone cesarean delivery.1 This is borne out in this study with 92% of all cases of uterine rupture occurring in such patients. The advantages of successful VBAC are reduced use of hospital resources and decreased maternal morbidity compared with repeat elective cesarean delivery.4 On the other hand, a failed VBAC results in increased maternal morbidity compared with repeat elective cesarean delivery or successful vaginal delivery.16,17 The most dramatic essence of the debate, however, surrounds the rare case of uterine rupture.
This population-based study helps delineate that risk by comparing the outcome of complete uterine rupture with dehiscence during a 10-year period when VBAC was encouraged in one province. The VBAC rate (31%) and the rate of success (80%) are in keeping with other North American studies.4,18,19 When the consensus groups in Canada and the United States endorsed VBAC, it was in women with one previous low transverse cesarean delivery.2,3 As success rates were reported, the indications were widened by many to include women with more than one previous cesarean delivery9,10 and to allow induction and augmentation of labor.5,6 Induction of labor remains controversial, although some studies have suggested that this is a reasonable practice.5,6 However, recent larger studies have shown an increased risk with the use of oxytocic agents to induce labor, particularly prostaglandins.4,7,8,11,12,14 Our data do not allow the precise degree of risk with the individual types of induction, but the fact that oxytocic agents for induction or augmentation of labor were involved in 43% of complete and 40% of dehiscence highlights the potential risk. Similarly, ten of 39 (26%) of uterine ruptures in this study were associated with more than one previous cesarean delivery. All cases of complete uterine rupture were clinically apparent, with abnormality of the fetal heart rate being the most common diagnostic aid, in keeping with other reports.13,19 Bleeding and pain were the other most common manifestations, and pain was noted even with regional anesthesia.20 Dehiscence of a previous cesarean scar is much less traumatic, and 52% of our patients were without symptoms and discovered en passant only at the time of repeat cesarean delivery. The perinatal outcome with dehiscence was almost universally good with no serious sequelae. However, with complete uterine rupture there was, excluding lethal anomalies, one perinatal death, one-third of neonates with severe asphyxia, but no infants with long-term postasphyctic sequelae in 4516 VBAC attempts.
These population-based results of uterine rupture during a 10-year period when VBAC was encouraged throughout the province are relatively reassuring. However, the potential maternal and perinatal sequelae of complete uterine rupture are such that all women considering VBAC must be informed of these possible, albeit rare, risks.21 Extending the indications for VBAC to include women with more than one previous cesarean delivery or the use of oxytocics can only be justified under special circumstances in hospitals with available personnel and facilities for immediate cesarean delivery and with fully informed consent.
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