There is a continuing debate on the optimal cesarean delivery rate and the following risks and benefits for both the mother and the newborn. In 1985, World Health Organization recommended that national rates of cesarean deliveries should not exceed 10% to 15% of live births1; however, it was recently stated that each country should aim for an optimal national rate rather than adopt a universal one.2 In many countries, cesarean delivery rates are substantially higher: in England approximately 26.5%,3 in Canada 25.6%,4 and in the United States approximately 31.9%.5 The dictum “once a cesarean always a cesarean” may have partially contributed to the high rates of cesarean deliveries.6
Hence, the National Institutes of Health, in the United States, convened a consensus conference to examine the safety and outcomes of Trial of Labor After Cesarean delivery (TOLAC) and recognized it as a reasonable option for many women with previous cesarean delivery.7 As a result, TOLAC could be used as an alternative to elective repeat cesarean delivery, in pregnant women belonging to group 5 of the Robson classification system (previous cesarean delivery, singleton, cephalic ≥37 weeks' gestation).8 The success rate of TOLAC (or vaginal birth after previous cesarean birth [VBAC]) may be as high as 72% to 75% of cases.9,10 These rates vary based on the demographic and obstetric characteristics of the women. Hence, factors that negatively influence the chance of a successful VBAC include increasing maternal age, high body mass index, high birth weight, and advanced gestational age at delivery (>40 weeks).11–18 A reduced success rate of VBAC is also documented in cases of preeclampsia and shorted interdelivery intervals.19,20 On the other hand, previous vaginal birth, especially successful VBAC, is the strongest predictor of success, with VBAC rates of 87% to 91% in that group.11,21–23
The aim of this review is to summarize evidence of consensus and controversy between 3 published national guidelines on VBAC and to focus, specifically, on the antenatal and intrapartum care of pregnant women with a previous cesarean delivery.
The most recent published clinical guidelines, statements, and practice bulletins by the Royal College of Obstetricians and Gynaecologists (RCOG 2015),24 the American College of Obstetricians and Gynecologists (ACOG 2017),25 and the Society of Obstetricians and Gynaecologists of Canada (SOGC 2005)26 were reviewed and compared; then a descriptive review was conducted. A summary of recommendations of the 3 guidelines is presented on Table 1.
All 3 guidelines recommend the implementation in antenatal counseling of a VBAC clinical pathway for women with a history of cesarean delivery.24–26 They promote a shared decision making and clear documentation in the pregnancy notes. Especially, the women should be informed on the potential risks and benefits of both VBAC and elective cesarean delivery by a member of the maternity team. Many of the factors related to the chance of a successful VBAC or the risk of uterine rupture are already known early in pregnancy27–29; however, the risks or benefits of VBAC may change as the pregnancy progresses. In addition, a VBAC calculator may be used to provide more specific information about the chance of a successful VBAC. A discussion regarding the option of VBAC should ideally take place early in gestation and in most of the cases the decision regarding the mode of delivery should be finalized by 36 gestational weeks.
Cochrane reviews suggest that there are both benefits and risks associated with either a planned repeat cesarean delivery or a planned induction of labor in women with a prior cesarean delivery.30–32 Women should be informed that planned VBAC is associated with approximately 0.5% risk of uterine rupture.33 Most of the maternal morbidity related to VBAC occurs when a cesarean delivery is eventually necessary.34–37 Thus, a successful VBAC is associated with fewer complications than elective repeat cesarean delivery, whereas a failed VBAC is associated with more complications.34–36,38 Moreover, a meta-analysis showed that the overall risk of perinatal death is higher in women attempting VBAC (odds ratio [OR], 1.71; 95% confidence interval [CI], 1.28–2.28).39 On the contrary, women should be informed that elective repeat cesarean delivery is associated with a higher risk of placenta previa in future pregnancies24 and respiratory problems of the newborn (6%).40 Furthermore, an increased risk of maternal mortality (1.3/10000) with elective repeat cesarean delivery compared with planned VBAC (0.4/10000) has been reported by several studies.33,35 According to the AHRQ meta-analysis, the rates of hysterectomy, thromboembolic disease, transfusion, and endometritis do not differ significantly between planned VBAC and repeat cesarean delivery.33
In addition, all guidelines approve a planned VBAC for the majority of women carrying a singleton pregnancy with a cephalic presentation at 37+0 weeks or beyond who have had a single previous lower segment cesarean delivery, with or without history of previous vaginal birth.24–26 As shown by systematic reviews, planned VBAC is a safe and appropriate mode of delivery for women with prior cesarean delivery.30,31,33 Moreover, evidence suggests that women with at least a 60% to 70% likelihood of achieving a VBAC experience the same or less maternal morbidity than women who have an elective repeat cesarean delivery.41,42 In cases of a breech presentation, the ACOG and the SOGC both state that external cephalic version is not a contraindication in candidates for VBAC, whereas there is no specific comment in the RCOG guideline.
The RCOG states that women who have had 2 or more prior lower segment cesarean deliveries may be offered VBAC after appropriate counseling by a senior obstetrician,24 whereas the SOGC states that VBAC may be successful in women with more than 1 previous cesarean delivery, but they note that it is associated with a higher risk of uterine rupture.26 Finally, the ACOG mentions that it is reasonable to consider women with 2 previous cesarean deliveries to be candidates for VBAC.25 Two large studies with sufficient size to control for confounding factors reported on the risks for women with 2 previous cesarean deliveries undergoing VBAC.43,44 One study found no increased risk of uterine rupture (0.9% vs 0.7%) in women with one versus multiple prior cesarean deliveries,44 whereas the other showed a higher risk of uterine rupture (1.8%) in women with 2 prior cesarean deliveries.43 There are limited data regarding the risks of VBAC after more than 2 previous cesarean deliveries.45 A systematic review suggested that women with 2 previous cesarean deliveries should be counseled about the success rate (71.1%) and the uterine rupture rate (1.36%) of attempted VBAC.46 The rates of hysterectomy (5.6/1000) and transfusion (1.99%) were increased in women with VBAC after 2 previous cesarean births.46
Special care should be taken in certain circumstances. The RCOG states that there is uncertainty about the safety and efficacy of a planned VBAC in pregnancies complicated by post-dates, twin gestations, fetal macrosomia, antepartum stillbirth, or maternal age of 40 years or more.24 However, according to the ACOG and the SOGC, fetal macrosomia, gestation beyond 40 weeks, twin gestation, and obesity are not contraindications for VBAC.25,26 One study47 showed an increased risk of uterine rupture beyond 40 weeks of gestation, whereas other studies have not found this association.48 As for twin gestations, various studies have reported similar rates of successful VBAC in twins (45% to 84%) compared with singleton pregnancies.49–52 In addition, birth weight of 4 kg or more is associated with an increased risk of uterine rupture (OR, 2.62; 95% CI, 1.001–6.85), unsuccessful VBAC (OR, 2.47; 95% CI, 1.82–3.34), and shoulder dystocia (OR, 25.13; 95% CI, 9.31–67.86).53 Moreover, maternal age of 40 years or more is an independent risk factor for stillbirth and unsuccessful VBAC.27,28,54 It should also be noted that, according to the SOGC, diabetes mellitus is not a contraindication for VBAC, whereas there is no guidance on this issue by either the RCOG or the ACOG.
Regarding the contraindications for attempting VBAC, all guidelines state that women with a history of uterine rupture, classical cesarean scar, or uterine surgery, during which the uterine cavity has been breached, are considered as high risk for uterine rupture and should avoid VBAC. In addition, in women with complicated uterine scars, caution is needed and decisions should be individualized by a senior obstetrician who has access on the details of the previous surgery. Obviously, VBAC should also be avoided in cases when other conditions that constitute absolute contraindications to vaginal birth are present (eg, placenta previa). A systematic review reported that women with 1 or 2 cesarean deliveries present with a 1% and 1.7% risk of placenta previa, respectively, in subsequent pregnancies.33 This was also confirmed by the findings of a recent meta-analysis.55
All 3 guidelines state that VBAC should take place in a suitably staffed and equipped delivery resource, available for immediate cesarean delivery and neonatal resuscitation. The ACOG alone, further states that home birth is contraindicated for women undergoing VBAC. Continuous fetal heart rate monitoring is recommended during labor, whereas regarding analgesia, epidural analgesia is neither contraindicated nor necessary. A recent meta-analysis has proven that in all labors, epidural analgesia increases the risk for assisted vaginal delivery (risk ratio, 1.44; 95% CI, 1.29–1.60).56 As for VBAC specifically, there is conflicting evidence: the National Institute of Child Health and Human Development study showed that epidural analgesia increased the success rate of VBAC,11 whereas other studies reported contradictory findings.57,58 An increasing requirement of pain relief in labor should raise awareness of the possibility of an impending uterine rupture. A consortium on safe labor found that women at term in spontaneous labor with VBAC have a similar labor curve with nulliparous women.59
Regarding induction or augmentation of labor, the RCOG states that women have a 2-fold to 3-fold higher risk of uterine rupture and approximately 1.5-fold higher risk of cesarean delivery in cases of an induced or augmented labor.24 The ACOG states that induction of labor remains an option,25 whereas the SOGC notes that oxytocin for induction should be used carefully.26 A study of 20,095 women found a rate of uterine rupture of 0.52% in VBAC with spontaneous labor, 0.77% for labor induced without prostaglandins, and 2.24% for prostaglandin-induced labor.60 The RCOG also states that induction of labor using mechanical methods (amniotomy or Foley catheter) is associated with a lower risk of scar rupture compared with induction using prostaglandins, whereas the ACOG and the SOGC mention that mechanical methods may be an option for VBAC in cases of an unfavorable cervix. As for prostaglandins' use for cervical ripening, the SOGC states that they should not be used, whereas the ACOG is against the use of misoprostol, but they found it difficult to make recommendations regarding the use of prostaglandin E2. In the National Institute of Child Health and Human Development study, induction with prostaglandins was associated with a higher uterine rupture risk (0.87%) and a related higher risk of perinatal death (0.11%).6 A recent Cochrane review concluded that evidence from randomized controlled trials on methods of induction of labor for women with a prior cesarean delivery is inadequate and existing studies were underpowered to detect clinically relevant differences for many outcomes.61 As for the augmentation of labor, both the ACOG and the SOGC state that oxytocin augmentation is not contraindicated and may be used in VBAC. A large multicenter study showed that augmentation or induction of labor is associated with an increased risk of uterine rupture (1.4% for induction with prostaglandins with or without oxytocin, 1.1% for oxytocin alone, 0.9% for augmented labor, and 0.4% for spontaneous labor).35
According to the RCOG, women in preterm labor should be informed that VBAC in this case carries a lower risk of uterine rupture compared with term pregnancies. The ACOG states that VBAC may be judged appropriate for women with second trimester preterm delivery or delivery after fetal death, whereas the SOGC makes no relevant statement. A study showed that planned VBAC success rates for preterm and term pregnancies were similar (72.8% and 73.3%, respectively), but rates of uterine rupture (3.4/1000) and dehiscence (2.6/1000) were significantly lower in preterm VBAC.62
The number of references for each guideline range from 119 (SOGC) to 154 (ACOG) with dates of publications between 1916 and 2017. All the guidelines state that the specific recommendations were developed after an extensive search of electronic databases. Furthermore, the quality of evidence is described using the GRADE system by the RCOG, the ranking system of the US Preventive Services Task Force by the ACOG, and the Evaluation of Evidence criteria outlined in the Report of the Canadian Task Force on the Periodic Health Exam by the SOGC. Expert consensus as a method of recommendation was performed, and all rated the strength of their recommendations. Only the RCOG suggested audit topics, which are represented in Table 2.
Many women will have to opt on the mode of delivery for a subsequent pregnancy after a cesarean delivery. Both alternatives—VBAC or planned cesarean delivery—present risks and benefits. Involvement of the pregnant woman, her family, and the obstetrician or other obstetric care provider on the final decision is strongly supported. The strengths of this review include the synthesis of the major guidelines in the recommendations for VBAC including antenatal and intrapartum care. However, there are certain limitations. First, the review is limited to 3 English language national guidelines, but the aim of this study is to compare guidelinesfrom similarly resourced settings. Second, the publication dates of the guidelines differ, which may have an impact on their recommendations, which are based on up-to-date studies.
To summarize, the existing evidence suggests that planned VBAC exposes the pregnant woman to a 0.25% additional risk for perinatal mortality or serious neonatal morbidity and an additional 1.5% risk of any significant morbidity compared with an elective repeat cesarean delivery, after 39+0 gestational weeks. However, it seems helpful to emphasize to women that the absolute risk of delivery-related perinatal death associated with VBAC is extremely low (0.04%) and comparable with that of nulliparous women.63,64 As a result, VBAC is a good alternative to cesarean delivery with high safety and efficacy rates.
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