Delivery after a previous cesarean section reviewed

At the start of the 20th century, cesarean section (CS) was uncommon in obstetrics. By the end of the century, CS rates had increased dramatically worldwide. Although the explanation for the increase is multifactorial, a major driver in the ongoing escalation is the increase in women who are delivered by repeat CS. This is due, in part, to the fact that there has been a sharp fall in vaginal birth after CS (VBAC) rates as fewer women are offered a trial of labor after CS (TOLAC), due principally to fears of a catastrophic intrapartum uterine rupture. This paper reviewed international VBAC policies and trends. A number of themes emerged. The risk of intrapartum rupture and its associated complications is low and may sometimes be overestimated. Individual maternity hospitals in both developed and developing countries are inadequately resourced to safely supervise a TOLAC. Efforts to mitigate the risks of TOLAC by careful patient selection and good clinical practices may be underutilized. Given the serious short‐term and long‐term consequences of rising CS rates for women and for maternity services generally, a review of TOLAC policies worldwide should be prioritized and consideration given to convening a Global Consensus Development Conference on Delivery after CS.


| INTRODUC TI ON
During the 1970s, the cesarean section (CS) rate in the US trebled to 15.2% and this was closely paralleled in other developed countries. 1Concerns about the rising CS rate led the National Institutes of Health (NIH) to convene a Consensus Development Conference on Cesarean Childbirth in September 1980.It concluded that the two major reasons for the increase were dystocia and prior CS.From 1970 to 1978 in the US, dystocia accounted for 30% of the increase in CS and prior CS accounted for 25%-30%.
In the past in the US, more than 98% of women underwent a repeat CS for any subsequent delivery because obstetricians continued to adhere to Craigin's mantra from 1916: "Once a cesarean, always a cesarean". 2However, in 1916 the CS uterine incision was usually vertical and low transverse incisions did not come into vogue until after the 1920s.
The Conference reviewed international studies on the safety of trial of labor after CS (TOLAC) after a previous low transverse TURNER incision and made six separate recommendations supporting a trial of labor.Guidelines from the American College of Obstetricians and Gynecologists (ACOG) subsequently endorsed a policy of TOLAC in women with one previous low transverse scar. 3,46][7][8] In contrast, there is less consensus about the management of women with a single previous low transverse CS.
Differences in obstetric opinions were relatively unimportant until the 1970s when overall CS rates were low and few women presented for antenatal care with a history of one previous CS. 9

| R ATE S OF VAG INAL B IRTH AF TER CE SARE AN S EC TI ON ( VBAC)
Following the NIH report and the ACOG guidelines, the VBAC rate in the US increased.From 1989 onwards, data on VBAC were collected on US birth certificates nationally.By 1990, the rate of VBAC increased to 21% and peaked subsequently at 30.2% in low-risk women in 1996. 10 1996, a Canadian study from 27 hospitals (two tertiary) in Nova Scotia reported that women with a previous CS who underwent a trial of labor were twice as likely to have major complications as women who had an elective CS. 11 The information was abstracted for 1982-1992 from medical records and discharge summaries before coding by trained personnel.However, there were only 10 cases of uterine rupture and details such as the type of uterine scar, the use of oxytocics, and hospital setting were not reported.After the publication of this paper, the ACOG updated their practice bulletin and advocated a standard of immediate surgical availability to provide care and emergency delivery during a TOLAC.
A Sounding Board in the New England Journal of Medicine (NEJM) from Bostonian obstetricians on the risks of lowering CS rates cited a risk of uterine rupture of "approximately" 1%. 12 It reported that the incidence of uterine rupture had tripled in Massachusetts between 1985 and 1995 but acknowledged that there was uncertainty as to whether the women had a previous CS or not.Nonetheless, the authors strongly recommended that a TOLAC should not be mandated for women with a previous CS, particularly if an emergency CS cannot be performed.The Centers for Disease Control (CDC) later reported that, after 1996, VBAC rates in both low-and high-risk patients in the US started to decrease. 10 2001, a large study was reported from 1987 to 1996 of 20 095 women with a previous CS in Washington state using state-wide linked databases. 13It concluded that the risk of uterine rupture was higher in women who had labor induced than in women who had a repeat elective CS.Induction with a prostaglandin conferred the highest risk.This study, however, had limitations.It excluded women with a previous vaginal delivery which is associated with a lower rate of rupture. 8The authors acknowledged that they were unable to document the accuracy of coding for induction or the severity of the ruptures. 13Surprisingly, they also reported no ruptures in 272 women with a previous vertical incision but 11 ruptures in 6980 women who had a prelabor repeat CS.This paper was accompanied by an editorial in the NEJM on the risk of VBAC. 14After considering the risks and benefits of a TOLAC, the editor concluded that his unequivocal advice to a patient would be to have an elective repeat CS.
The ACOG Practice Bulletin in 2004 continued to support TOLAC but retained the immediate surgical availability statement.This proved controversial as a multidisciplinary guideline concluded that TOLAC should not be restricted to facilities with available surgical teams present throughout labor, because there was insufficient evidence that this improves outcomes. 15 December 2004, a prospective cohort study from 1999 through 2002 at 19 NIH academic hospitals reported that a TOLAC is associated with a greater perinatal risk than elective repeat CS without labor, although absolute risks were low. 16TOLAC ranged from 19% to 63% between hospitals and declined during the study from 48.3% in 1999 to 30.7% in 2002.The study concluded that the risk of an adverse perinatal outcome at term was greater with TOLAC than with elective CS, albeit small (0.46/1000).
Women presenting in early labor who underwent CS were excluded from the analysis. 16Women with more than one previous CS were included in both groups, including 5.5% in the TOLAC group and 38.2% of the repeat CS group.All types of previous uterine scars were included and 0.5% of women had an unknown type.Cases of asymptomatic uterine dehiscence were included in both groups.The use of oxytocics was high in the TOLAC group.There were two maternal deaths related to the mode of delivery, both in the elective CS group.
All 12 cases of hypoxic ischemic encephalopathy (HIE) were in the TOLAC group but no details or follow-up were provided.There were more antepartum stillbirths in the TOLAC group before 39 weeks of gestation (16 vs. 5, P = 0.008) but these would not be prevented by an elective CS scheduled after 39 weeks.
Great caution should be taken in extrapolating this study to other maternity settings or circumstances.If women receive electronic fetal monitoring during their labor, the risk of HIE has been cited as 0.08% (8/10 000). 6The prospective risk of antepartum stillbirth beyond 39 weeks of gestation while awaiting spontaneous labor has been cited as 0.1% (10/10 000) which is similar to that in nulliparas. 68 In the German state of Hasse, after 1996, the VBAC rate after each of the papers fell from a peak of 47.9%.In two large hospital-based obstetric services in the capital of Ireland, the VBAC rate had been high at 64.4% in 1990.It, too, fell from 1996 after each of the papers, reaching 32.9% in 2014. 18This suggests that all three NEJM publications and the expert commentaries have had a "domino effect" on VBAC rates in other developed countries, even though there are differences in patient population and differences in healthcare systems.

| CONS ENSUS DE VELOPMENT CONFEREN CE 2 010
Concerns about the decline in VBAC rates and the rising CS rate overall in the US led the NIH to commission a review of the literature and to convene a Consensus Development Conference in March 2010 on delivery after CS. 19,20 It noted that fear of uterine rupture was the clinical reason frequently cited for avoiding a TOLAC.
The Agency for Healthcare and Quality (AHRQ), who had been commissioned by NIH, published their expert report on VBAC in 2010. 19The report reviewed 203 selected papers between 1966 and 2009 of US women with a singleton pregnancy who were eligible for a TOLAC or a repeat elective CS.The range of TOLAC rates was 28%-82% and VBAC rates in women who labored were 49%-87%.In patients who labor spontaneously, the VBAC in three large studies ranged from 52.6% to 74.0%, compared with 51.4% to 63% in women who had labor induced. 6,19The best predictors of women having a TOLAC were a previous vaginal delivery and antenatal care in a tertiary center.The risk of uterine rupture was "low at less than 1%".It concluded that given the available evidence, trial of labor was a reasonable option for women with one prior low transverse uterine incision. 20systematic review by WHO on the prevalence of uterine rupture in 86 groups of women found that it was lower in developed countries compared with underdeveloped countries. 21For women with a previous CS, the prevalence of rupture was reported as "in the region of 1%".
In 2010, ACOG updated its national guideline on VBAC to incorporate the data produced by AHRQ for the NIH conference. 15,20It cited a uterine rupture rate of 0.7%-0.9%with a trial of labor after one previous CS.If a uterine rupture occurred, it cited a 6.2% risk of HIE and a 1.8% risk of neonatal death.For women with one previous CS, it reported a 60%-80% chance of a VBAC following trial of labor.
In November 2017, a revised ACOG guideline noted the reports of uterine rupture and other complications associated with TOLAC and that "concerns over liability have a major impact on the willingness of physicians and healthcare institutions to offer trial of labor". 22Some hospitals had stopped offering TOLAC altogether.
A survey of ACOG Fellows showed that, between 2003 and 2006, 26% stopped offering a TOLAC even if the woman had a previous vaginal delivery. 20ter the 2010 conference, the VBAC rate in the US increased slightly from 9.7% in 2011 to 14.4% in 2021. 23From 2016 to 2018, VBAC rates increased in 17 US states, decreased in one, and did not change significantly in 32. 24It was estimated that if current VBAC trends continued, it would be 2030 before the US reached its 2020 goal of an 18.0% VBAC rate.
The decline of VBAC is also driving an increase in overall CS rates.
In the US, the repeat CS rate in 2021 was 85.9% in women with a previous CS and the overall CS rate had increased to 32.1%. 24The increased repeat rate has increased the overall CS rate.In Ireland, the overall rate reached 36.6% in 2021 with a historically low VBAC rate of only 18.1%. 25A recent review of 154 countries found that CS rates are rising in all regions and projected that, by 2030, 28.5% of women worldwide will give birth by CS. 26 When it comes to the management of delivery after a previous CS there are no gold-standard randomized controlled trials to inform practice and such trials are unlikely in the future due, for example, to the challenge of informed consent.It is a concern that a major transformation in maternity care globally within a generation is based on what is considered a low level of evidence with limited consensus between guideline developers. 7,8,270]

| RIS K OF UTERINE RUP TURE
The main fear regarding a TOLAC is intrapartum uterine rupture.In assessing risk, it is important to draw a sharp distinction between complete uterine rupture involving the full thickness of the uterine wall and incomplete rupture (dehiscence) where the visceral peritoneum remains intact because there are significant differences between the two in terms of clinical presentation and complications. 5risk of 1% has been cited by reports based on selected studies.The 2010 ACOG guideline reported a 0.7%-0.9%risk of rupture.This calculation was based on a small number of heterogeneous US studies in large academic hospitals.Risk was calculated based on studies that included women with more than one previous CS, different uterine scars, and term-only deliveries and that excluded women with a previous vaginal delivery. 19,20e ACOG guideline cites a risk of 0.7% for TOLAC at term based on the AHRQ report, which had identified only eight "good or fair quality" American studies. 19In the eight papers, the highest rate was 0.74% in 19 university hospitals which included women with more than one previous CS and any type of uterine scar.Only one of the eight studies confined itself to patients with a single prior low transverse CS and included women with a previous vaginal delivery. 28In this study, there were only four ruptures in 927 (0.4%) women who underwent a trial of labor.
A 1% risk of rupture with labor after one previous low transverse CS is higher than rates reported outside the US.0][31][32] In a large Irish teaching hospital, 75.6% of 5320 women with a previous single low transverse CS had a TOLAC under strict supervision in a wellstaffed delivery suite. 33The VBAC rate was 77.8% and the rate of rupture was 0.2%.It was only 0.1% if the woman went into spontaneous labor and did not receive oxytocin augmentation.Of the nine cases of rupture, there was no serious maternal or neonatal mortality or morbidity. 33 is possible to mitigate clinical risk with informed obstetric judgment.8]19,20 For example, avoiding induction of labor and the cautious use of oxytocin augmentation may decrease the risk of rupture.A previous vaginal delivery is associated with a higher VBAC rate and lower rate of uterine rupture. 8,19Predictive models have been developed to estimate the probability of a successful VBAC but have not yet been fully validated. 6woman also needs to be informed of the benefits of VBAC not only for the current pregnancy, but also to minimize the chances of a repeat CS for any future deliveries.The clinical factors associated with both an increased and a decreased probability of a successful TOLAC are well established.[5][6][7][8]19 Although the rates of TOLAC have decreased, the successful VBAC rates have remained around 60%-80% in those women allowed to labor.

| VARIATI ON S IN VBAC R ATE S
Healthcare setting matters for a TOLAC. 34Primary CS rates are lower in developing countries and, thus, fewer women present for delivery after CS.However, if a uterine scar ruptures, the associated adverse clinical outcomes are more likely in low-than in highresource countries.Most of the requirements for a safe TOLAC are barely met in resource-poor settings. 35 high-resource countries, there is wide variation between hospitals. 36In a study of CS rates in all 19 hospitals nationally, women with a previous CS were particularly subject to variable practice, especially for elective CS, even after accounting for case mix and sociodemographic differences.There was a decreased risk of both elective and emergency CS, with and without previous CS, in academic hospitals, which may reflect better staff resources.
In a study of 3207 hospital-based obstetric services in the USA where over 34 million births took place in 2010-2018, 37.4% of hospitals were low volume (<2000 births per annum). 37Half of the lowvolume hospitals were not within 30 miles of another hospital-based obstetric service.The median number of births per annum nationally was only 755 per hospital.Large-volume hospitals were more likely to be teaching hospitals, non-profit, and to have a neonatal intensive care unit.Information was not provided on staff resources.A lack of in-hospital trained midwifery, anesthetic, neonatal, and obstetric staff in a low-volume hospital is likely to increase the risk of a long rupture-emergency CS interval and thus increase the neonatal and maternal risks.This may explain why individual US hospitals and obstetricians no longer offer women a TOLAC.This raises the question as to whether women with one previous CS should be referred from a low-volume hospital to a high-volume hospital if she wants the option of VBAC.If perinatal networks can refer women to tertiary referral centers before labor in the fetal interest, why should they not also refer in the maternal interest when it may safely avoid repeat CS not only in the index pregnancy but potentially in future pregnancies?
It is also important to remember that planned elective CS does not guarantee rupture will be prevented in all women with a previous low transverse uterine incision because they may go into labor before the scheduled surgery.This is more likely to occur since obstetricians started deferring elective CS from 38 to 39 weeks gestation to prevent neonatal respiratory problems. 38In Ireland, for example, the dramatic fall in VBAC rates has not eliminated cases of uterine rupture. 25

| CON CLUS ION
Decisions regarding the obstetric management following one previous CS are best made by a woman in partnership with her obstetrician.The decisions have serious implications not only for the woman and her offspring in the short term, but also for any future pregnancies.To make good decisions, the risks of rupture need to be customized and precise, and not be overestimated.The benefits of VBAC should not be underestimated by discounting the advantages for subsequent deliveries.Women should be informed about how clinical risks can be mitigated and the importance of close supervision in labor.If it is practical, well-informed women who want a VBAC may need to be given the option of delivery in another hospital or by another obstetrician.A woman, her family, and her obstetrician need to confident that a TOLAC can be successfully managed.
On reviewing the literature and analyzing TOLAC and VBAC trends, the contemporary management of women with one previous figures in 2005.18In the German state of Hasse, after 1996, the