Sakala (2003), an expert in the field of scientific outcomes in the United States states that considering this report, every woman with a previous caesarean section should be given all the information she needs to make an enlightened choice and that research on this subject should continue.
On the other hand, the studies conducted to date are not without failings. Many of those quoted hereafter are criticised, even in the scientific reviews in which they are published. Thus, the American writer, Goer (2003), author of The Thinking Woman’s Guide to a Better Birth, talks of ‘Spin Doctoring the Research’, in the scientific publication Birth. Goer denounces not only the methodology employed for many of these studies – therefore questioning their conclusions – but also claims that the media propagated false outcomes. As a result, she says, not only health professionals but also pregnant women and couples expecting a baby were equally misled. This can be very harmful for the parents’ and their baby’s welfare.
This appears to have happened with a major study on VBAC, conducted by Lydon-Rochelle et al. (2001), which is discussed later in this chapter.
literature reviews were conducted for the American and Canadian consensus conferences (National Consensus Development Conference on Caesarean Birth, NIH, USA, 1980 and the National Conference on Aspects of Caesarean Birth, 1985, McMaster University, Canada). By ‘basic’ risk, I mean the risk associated with a spontaneous VBAC (without induction of labour). In 1986, for instance, the Canadian consensus conference, after conducting a literature review covering the preceding 25 years, concludes that the risk of a symptomatic separation of the uterine incision when having a VBAC is only 0.22% for women who had a previous caesarean delivery.
Many studies since that time have reported similar or relatively low rates, as is seen later.
It appears that the increasing risk of having a VBAC is the result of modifications in obstetrical practices; it does not mean that VBAC itself has become more dangerous. Recent studies tend to confirm this. Let us recall, in the first place, that when this option began to be encouraged at the end of the 1970s and in the beginning of the 1980s, physicians were more careful when prescribing drugs for induction of labour. The positions of medical associations confirm this. During the 1980s and the beginning of the 1990s, it seems that the use of drugs for artificially inducing or accelerating labour gradually increased, a practice that had not been adequately evaluated beforehand. This can also be said of many obstetrical practices or interventions. It is only at the end of the 1990s that studies raised the alarm. In addition, near the end of the 1980s, suture techniques in a caesarean delivery changed but, again, without having been sufficiently evaluated (Enkin and Wilkinson 2001). Until the 1990s, a double-layer suture for closing the uterine incision was usually done but some physicians were beginning to use a single-layer suture in order to shorten operating time. The latter technique was taught to interns in hospitals.
Even though a few studies were published on this topic during the 1980s, they were not very useful because the sampling used was too small, and the data on uterine ruptures were lacking. Recent studies, however, have attempted to evaluate the risks of uterine rupture according to the type of suture. In Canada, for example, Bujold et al. (2002a) claim that the single-layer suture multiplies by 4 to 6 times the risk of uterine rupture. Studies on VBAC risks conducted during the 1980s and 1990s, some of which included thousands of women, often confirm the outcomes of former studies on VBAC.
Rupture risk: a risk not only of VBAC but also of every caesarean
Rupture risk, which is often associated with VBAC, is present even in the absence of labour (women have had uterine ruptures before the onset of labour or before their planned repeat caesarean delivery). Thus, Wen et al. (2004) mention uterine rupture risk of 0.25% in women who had planned or had a repeat caesarean compared to a 0.65% risk for trial of labour. However, it is quite possible that these events increased with the development of labour-inducing drugs, such as the use of misoprostol, a drug primarily intended for other uses besides obstetrics, where it was introduced without prior evaluation.
What is dangerous and what is not?
According to Beckett and Regan (2001), most of the uterine ruptures mentioned in these studies are in fact dehiscences. Many studies make no difference between rupture and dehiscence, thus making it difficult to interpret the data collected.
A dehiscence is not as dangerous as a uterine rupture and does not even need to be repaired. According to Enkin et al. (2000), most dehiscences and uterine ruptures are asymptomatic and do not require treatment. It is possible that the risk of uterine rupture is lower than proposed because many studies make no difference between rupture and dehiscence. The other expressions for dehiscence
‘window’ or ‘thinning of the uterine segment’ do not mean the same thing as uterine rupture (Flamm 2001b).
What is uterine rupture?
A true uterine rupture therefore involves all the thickness of the uterine segment (all the layers including the serosa). It is symptomatic and needs to be repaired (Lieberman 2001). It is this type of rupture that may be dangerous for the mother and the baby. Part of the baby’s body or all of it can come out of the uterus and the baby then lacks oxygen. For the mother, there is a risk of haemorrhage and the possibility of having to undergo a hysterectomy.
It is clearly important to differentiate between a real rupture and dehiscence.
Kieser and Baskett (2002) found the rate of real ruptures to be 0.3% and that of dehiscence to be 0.5%. Induction of labour doubled the risk of a real rupture compared to that of dehiscence. In this study, 11 585 women had a prior caesarean delivery and among those who had attempted to have a vaginal birth (4516), it was possible to obtain the rates of real ruptures and of dehiscences.
Incidence of risk
The additional risk of uterine rupture in a woman attempting to have a VBAC compared to one having a repeat caesarean is lower than was previously believed.
Studies such as the one conducted in American birth centres (Lieberman et al.
2004) reveal a rate varying from 0.2 to 0.6% when labour is not induced or stimulated. Moreover, Chauhan et al. (2003), the authors of a systematic literature review published in 2003, state that the studies they reviewed reveal a uterine rupture rate of 0.6%.
The findings of meta-analyses
A meta-analysis is a study that combines the outcomes of controlled trials by regrouping them statistically. This is the highest level of what is considered as
‘scientific evidence’. The second level is a systematic review. Only two meta-analyses on VBAC risk were conducted between 1990 and 2000, the first one in 1991 and the second in 2000. The outcomes of these meta-analyses are contradic-tory. The explanation for this could be that they reflect the change in obstetrical practices. The meta-analysis of Rosen et al. (1991), based on studies published between 1982 and 1989, reveals no difference between the two options, repeat cae-sarean and VBAC, as to negative effects and advantages. The other meta-analysis
(Mozurkewich and Hutton 2000), published in 2000 and covering the 1989–1999 decade, states that there is a very slight increase of uterine rupture risk in a VBAC (compared to a repeat caesarean delivery), i.e. 0.4 vs. 0.2%. It emphasises the fact, however, that a VBAC could reduce maternal morbidity and slightly increase risk of complications for the baby, as compared to a repeat caesarean. Nonetheless, it concludes that one or the other option can be considered reasonable.
Several systematic reviews have also been published, among which that of Guise et al. (2004) explicitly mentioned risk of perinatal death in case of uterine rupture. This review reveals that it would require 370 elective caesarean sections to avoid one symptomatic uterine rupture in women who had a previous caesarean section, and that it would require 7142 planned repeat caesarean deliveries to prevent one perinatal death related to uterine rupture.
In the year 2000 and subsequently: two widely debated studies
Since the beginning of the present decade, the VBAC rate has continued to decrease. Studies published in the year 2000 and after may have accentuated this decline. Some suggest that these studies have weak points either in their methodology or in the analysis of outcomes and conclusions. To illustrate this opinion, I shall present two of them.
The Lydon-Rochelle et al. study on VBAC risks: are the conclusions misinterpreted?
During summer, in 2001, I was very surprised to hear in the media that a large-scale study on VBAC risks had come to the conclusion that VBAC is dangerous, as announced by Radio-Canada on July 5:
After a caesarean, better avoid a natural birth.
The study in question was conducted by researchers of Washington University (Lydon-Rochelle et al. 2001). It revealed, by using two diagnosis codes found in the medical records of more than 20 000 women who had given birth between 1987 and 1996, that 91 of them had experienced a uterine rupture. The rate of uterine ruptures without labour was 0.16%; with trial of labour (spontaneous onset) 0.52%;
with induction of labour without prostaglandins 0.77%; and it rose to 2.45% when labour had been induced with prostaglandins. These outcomes on the risk of using drugs for inducing labour confirmed those of studies published not long before the Lydon-Rochelle study (Zelop et al. 1999; Ravasia et al. 2000; Blanchette et al. 2001). The editorial of the New England Journal of Medicine accompanying the publication contained very negative remarks concerning VBAC. It seems that the media had retained only these remarks and not the conclusions of the study concerning factors that really increased VBAC risks.
Nevertheless, uterine rupture incidence for attempting a VBAC without induc-tion was similar in this publicainduc-tion to that obtained in other studies to date. Why
then did the media claim that it had been discovered that VBAC was dangerous, when for decades it was well known that there was a slight additional risk with a VBAC compared to a repeat caesarean delivery? This study raised a controversy.
A researcher who had conducted many studies on VBAC published in Birth, a paper in which he exposed the methodological failings of the study – namely the lack of reliability of the discharge records’ codes (Flamm 2001a). As a matter of fact, a publication of the Health Department of the State of Massachusetts had noted the lack of specificity of the code identifying uterine rupture and the lack of consistency when entering this code (Massachusetts Department of Health 2000).
Flamm (2001a) points out that it is preferable to check the data furnished by the codes with the obstetrical files of the women. Moreover, women’s groups defending women’s rights in childbirth and consumers’ groups fighting excessive caesarean rates also gave their opinion. This study had shown that it is when labour is induced, especially with prostaglandins, that it is dangerous to have a VBAC. However, the editorial and the media, for their part, had concluded that the risk is inherent to VBAC. Notwithstanding these outcomes on the risks of prostaglandins, 2 years later a survey of Canadian obstetricians–gynaecologists, who had conducted VBACs, revealed that a quarter of them would prescribe prostaglandins to induce labour (Brill et al. 2003).
The Lieberman et al. study on birth centres
The study of Lieberman et al. published in 2004 is a prospective study. It extended over a 10-year period and was conducted in 41 birth centres in the United States.
It concerned 1453 women who planned having a VBAC. It revealed a rather low rupture rate, i.e. 0.2% for the group of women considered as low-risk cases and 0.6% for those at higher risk. The latter group included women who had experienced more than one caesarean delivery or women who had given birth after 42 weeks of gestational age. Thus, the general rupture rate obtained was 0.4%, a rate similar to the one in studies published since the beginning of the 1980s and even prior to that. There were six uterine ruptures, three in the first group and three in the second. In the group of women considered as higher risk cases, two babies died and one woman underwent a hysterectomy. In the low-risk group, there were no negative effects for the mothers but three babies died. The deaths had nothing to do with VBAC; they were due to shoulder dystocia and cord prolapse with footling breech birth and placental abruption. In the case of cord prolapse, transfer to hospital took 3 minutes but the hospital took 24 more minutes before performing the caesarean. As for the case of placental abruption, the transfer lasted one hour and it took another hour before the caesarean could take place. Notwithstanding the delays encountered in hospitals and the low incidence of uterine ruptures, the authors of this study came to the conclusion that it is dangerous for a woman to have a VBAC outside a hospital setting. This conclusion was criticised (Johnson and Daviss 2005).