Anesthesia providers may have varying degrees of familiarity with certain terms relevant to this topic that are often used in conflicting and confusing ways by obstetricians, family practitioners, nurse midwives, investigators, and expecting couples. The following definitions and acronyms are offered to promote clarity and to provide consistency throughout this discussion (3,6):

The past four decades have seen a remarkable swing of the pendulum regarding overall CD rates and VBAC in the United States, and worldwide. Cesarean delivery represents the most commonly performed surgical procedure in the United States. According to data from the National Center for Health Statistics, nearly one-third (32%) of all births in 2007 were cesarean deliveries (7) (Fig. 10-1). This rate represents an all-time high. The United States CD rate was approximately 5% in 1970 and has been rising since with ever-increasing prospects. The VBAC rate has played an important role in this trend: When recommendations favoring TOLAC were published by ACOG in 1988 and 1994, the number of women delivering by VBAC with a prior CD rose from 5% in 1985 to almost 29% in 1996, and the total CD rate declined to 20%. Since then, reports of increasing uterine rupture and TOLAC complications in an
adverse medicolegal climate and large epidemiologic studies documenting the maternal–fetal safety of PRCD dissuaded many obstetricians and expecting couples from attempting TOLAC. US data from 2006 show that only 8% of women with prior CD delivered by VBAC. It appears that modern obstetrics has returned via a convoluted path to Dr. Cragin’s century-old dictum (8,9).

Several factors contribute to the increased rate of cesarean delivery. Roughly one-third of nulliparous women undergo operative delivery (10). In addition, an estimated 40% of cesarean deliveries performed are planned repeat procedures. PRCD performed due to a previous scar is the most commonly cited reason for cesarean delivery (11). The coinciding decrease in the number of TOLAC attempts also significantly contributes to the overall increase in the rate of cesarean delivery (3). Other contributing factors include changes in practice environment such as the introduction of electronic fetal monitoring, the extinction of vaginal breech deliveries, and the declining use of operative vaginal deliveries (12,13,14). There is an ever-growing body of evidence providing clinical reasons to substantiate the increased performance of CD. Nonetheless, the short- and long-term benefits and risks presented to both mother and infant have been the subject of intense debate for several decades (15). Similarly, the mode of delivery for subsequent pregnancy among women who have undergone a previous CD has divided the scientific community for years.

VBAC is not a novel concept. There are reports of successful VBAC dating back to the 1950s in Europe—the United Kingdom in particular. Publications addressing the appropriateness of VBACs have ranged from isolated case reports to large clinical trials. VBAC has been widely practiced in UK since the standardization of the low transverse (Kerr) hysterotomy as the incision of choice (16). However, it was not until the time period spanning from 1981 to 1996 that US obstetric providers really embraced this practice. During that time, VBAC grew in popularity in the United States primarily due to concerns regarding the growing cesarean delivery rate. In 1982, the first statement published after the National Institutes of Health Consensus Conference endorsed VBAC as being an “acceptable option” to repeat cesarean delivery for many women. It was then stated that measures should be taken to ensure careful selection of patients, proper facilities, and immediate availability of appropriate staff including in-house obstetrician and anesthesia provider (17). At its peak in 1996, VBAC rates were reported to be more than 28% in the United States. These rates were short-lived though as concerns quickly grew about the potentially serious complications of TOLAC (18). Quite notably, there was marked concern regarding adverse outcomes associated with failed TOLAC including but not limited to uterine rupture, hysterectomy, transfusion, maternal, and perinatal mortality. The current VBAC rate in the United States is reported to be approximately 8.5% (19). Concerns about patient safety and physician liability have thus led to more restrictive policies and the coinciding decline in VBAC use in the United States.

TOLAC rates are highly variable; they range from 28% to 70% with an overall US rate of 58% (20). The Royal College of Obstetricians and Gynaecologists (RCOG) reports a successful VBAC rate of 72% to 76% after one cesarean delivery (5). A Canadian study reported similar results, citing a VBAC success rate of 76.6% (21). Globally speaking, TOLAC results in VBAC 60% to 80% of the time although physicians in Europe, Asia, and Africa are more inclined than those in the United States and Canada to attempt TOLAC (22). There are several factors—medical and non-medical—that can be used as predictors of VBAC success and hence influence VBAC practice patterns. Practice patterns may vary according to geographic region, hospital setting, provider preference, and patient characteristics. VBAC has an inverse relationship to CD rates; high VBAC rate is invariably associated with lower CD rates (23). Geographically speaking, recent data trends suggest that Southern states have the lowest VBAC rates and Western states have the highest VBAC rates (23,24,25). In terms of hospital setting, TOLAC is more likely to be attempted in hospitals with higher delivery volumes, academic tertiary care centers, and teaching hospitals with residency programs. As a result, lower rates of cesarean delivery are observed in such facilities (26,27). A study by DeFranco et al. further demonstrates greater VBAC attempts
at university and community hospitals with obstetrics training programs than in community hospitals without training programs (61% vs. 50.4%). The success rate across all hospital types was reported to be 75% (28). In terms of provider type, VBAC success has been reported by both obstetricians and clinicians who are not obstetricians. Specifically, a recent national study has reported successful VBAC rates of 81% and 87% respectively for family practitioners and certified nurse midwives. For obstetricians, the reported VBAC success rate for women having TOLAC was 65.4% (22,29). According to survey data from ACOG members, US obstetricians are performing “fewer VBACs due to concern about liability, patient preference, and limited resources at their delivery hospitals” (22,30,31). Leading authorities in US obstetrics have publicly raised valid concerns over management of TOLAC parturients by anyone other than experienced obstetricians in a facility with immediately available staff for emergency care.

It is also important to consider how certain patient characteristics and obstetric factors may have an effect on VBAC practice patterns. Specifically, several studies identify maternal age, race/ethnicity, and economic status as being demographic factors affecting TOLAC rates (20,29). There has been a decrease in VBAC use across all age groups (18,19). Similarly, the VBAC rate has declined for all racial and ethnic groups (19,23,25). It is interesting to note, however, that non-white women are more likely to attempt TOLAC but less likely to be successful at VBAC (32). In terms of obstetric factors, women with a prior vaginal delivery had greater than twice the chance of a TOLAC (odds ratio: 1.51 to 6.67) (23,33,34,35). Eleven cohort studies consistently reported that a prior history of vaginal delivery increases the chance of VBAC (35,36,37,38,39,40,41,42,43,44,45). Furthermore, women with a history of prior VBAC were three to seven times more likely to have a VBAC for their current delivery compared with women with no prior vaginal deliveries (38,40,41,42,43,44,46,47). As alluded to earlier, non-clinical factors are influential and relate to the likelihood of TOLAC. NIH data suggest variance in VBAC rates by insurance status; privately insured women have lower VBAC rates and higher cesarean delivery rates than their Medicaid counterparts (26). Contrarily, analyses of datasets from the Nationwide Inpatient Sample (NIS) for years 2000, 2003, and 2005 found no difference in VBAC process measures by insurance type. It has been postulated that the low use of VBAC is independent of insurance type but rather it is dependent upon hospital resources (23,34). The interaction of the many factors—medical and non-medical—that influence TOLAC utilization and VBAC practice patterns are quite complex and constitute an important component in decision-making and quality of patient care. Certainly, a better understanding of these factors and the significance of their impact on TOLAC/VBAC is warranted (20).

There are several (absolute or relative) contraindications to TOLAC: Unavailability of staff for emergency abdominal delivery (home birth, understaffed small hospital), general contraindications to labor or vaginal delivery (e.g., placenta or vasa previa, obstructed birth canal [e.g., fibroids], active herpetic infection in the birth canal, severe maternal cardiovascular pathology, intrapartum malpresentation [singleton or multifetal], Ehlers–Danlos syndrome type IV), prior uterine perforation or open fetal surgery, prior hysterotomy with any vertical component (documented or suspected by history), transmural myomectomy, cornual resection (for interstitial ectopic), prior uterine rupture or hysterotomy scar dehiscence, congenital uterine anomaly with or without metroplasty, three or more previous CD, two previous CD without vaginal delivery, prior shoulder dystocia, fetal macrosomia (estimated fetal weight >4 kg), maternal obesity, short stature, and post-term induction of labor (or combinations thereof—in order of decreasing criterion firmness) (48,49) (Table 10-1).

The risk of symptomatic uterine rupture during TOLAC varies considerably by prior hysterotomy type: It is 0.2% to 1.5% with Kerr (low transverse), 1% to 7% with Krönig (low vertical) and 4% to 9% with classical/T/J-shaped incisions (Fig. 10-2). As most expecting couples and obstetricians in the United States consider a risk of catastrophic uterine rupture greater than 1% to be excessive, in practical terms only women with prior known or estimated Kerr hysterotomy are considered TOLAC candidates. Limited literature has addressed the issue of mode of delivery among women with two prior Kerr hysterotomies and prior vaginal delivery; it suggests that these women have similar chance of successful VBAC and moderately increased major morbidity when compared to women with one prior CD. Thus, ACOG now states that women with two previous Kerr hysterotomies may be considered TOLAC candidates (6).