What was the Canadian Term Breech trial?

A student midwife asked: “I have seen mention of the Canadian term breech research in journals, but googling this just takes me to various studies, and I know this was controversial research that was criticised but as I don’t know the history or how they fit together, I don’t know where to start with reading the critiques.  Is there a good overview?”

Yes, and you’re absolutely right; I couldn’t easily find a ‘beginner’ online overview either, so here we go. 

Just bear in mind that, like any story, this is told from my perspective, and others would tell it differently, or prioritise different elements of it.

What was the Canadian Term Breech Trial?

The Canadian term breech trial was a study which began in 1997 with the aim of seeing whether vaginal birth or caesarean section was the safest option for babies who were presenting by the breech (that is, bottom first).

The lead researchers (Hannah et al 2000) were based at the University of Toronto in Canada.

The idea was to assign women whose baby was breech randomly to ‘vaginal birth’ or ‘caesarean section’ in a randomised trial and then to look at the outcomes. We could then find out how many of the women and babies in each group were alive and well, look at who had problems and compare these within the two groups, thus finding out if one of these practices was safer and/or better than the other. 

Because serious problems are (happily) quite rare, researchers need as many people as possible in their studies in order to get good data, so this was a multi-centre trial, which means that data is collected from lots of other centres (in this case hospitals) around the world.  In total, 26 countries contributed data to this study.

Originally, the research was going to continue for five years, but the researchers decided to stop the trial early and publish the results, because they felt that the data was showing that caesarean section was a far better and safer option than vaginal birth for breech babies. 

So what did they find?

The results were published in The Lancet (Hannah et al 2000) and here’s the abstract:

BACKGROUND: For 3-4% of pregnancies, the fetus will be in the breech presentation at term. For most of these women, the approach to delivery is controversial. We did a randomised trial to compare a policy of planned caesarean section with a policy of planned vaginal birth for selected breech-presentation pregnancies.

METHODS: At 121 centres in 26 countries, 2088 women with a singleton fetus in a frank or complete breech presentation were randomly assigned planned caesarean section or planned vaginal birth. Women having a vaginal breech delivery had an experienced clinician at the birth. Mothers and infants were followed-up to 6 weeks post partum. The primary outcomes were perinatal mortality, neonatal mortality, or serious neonatal morbidity; and maternal mortality or serious maternal morbidity. Analysis was by intention to treat.

FINDINGS: Data were received for 2083 women. Of the 1041 women assigned planned caesarean section, 941 (90.4%) were delivered by caesarean section. Of the 1042 women assigned planned vaginal birth, 591 (56.7%) delivered vaginally. Perinatal mortality, neonatal mortality, or serious neonatal morbidity was significantly lower for the planned caesarean section group than for the planned vaginal birth group (17 of 1039 [1.6%] vs 52 of 1039 [5.0%]; relative risk 0.33 [95% CI 0.19-0.56]; p<0.0001). There were no differences between groups in terms of maternal mortality or serious maternal morbidity (41 of 1041 [3.9%] vs 33 of 1042 [3.2%]; 1.24 [0.79-1.95]; p=0.35).

INTERPRETATION: Planned caesarean section is better than planned vaginal birth for the term fetus in the breech presentation; serious maternal complications are similar between the groups.

So what happened next?

Almost as soon as it had been published, however, other researchers, practitioners and consumer groups began to spot problems with the methods that had been used to carry out the research. 

They realised that there were so many issues with the way in which the research was designed and carried out that its findings could not be relied upon. 

People started to publish critiques and articles discussing these, and the conversation grew and grew. 

Here’s some of what I wrote at the time:

“Despite the fear created by this research, as Michel Odent pointed out, the summary of what we learned from the Canadian term breech trial is that, “a breech birth in a conventional hospital and in the presence of an obstetrician is dangerous” (Odent 2003: 11).

“For anyone who missed it, this trial compared the difference between actively managed vaginal breech delivery (with lots of manoeuvres performed on women lying on their backs) and caesarean section. Perhaps unsurprisingly, caesarean section ‘won’ this comparison, an outcome which is less of a bombshell if one looks at the study methods.

“Firstly, the results of this study were analysed by “intention to treat”. This meant that the data on the 43.3% of women who were randomised into the vaginal birth group but who actually had a caesarean (a statistic which, in itself, might tell you something about the “keen-to-intervene” philosophy held by those involved in the trial) was analysed as if those women had given birth vaginally. Without going into too much depth about research philosophy, there is a justification for analysing the results this way, but it would have been very useful if the researchers had also included an analysis of the results by actual mode of birth.

A large proportion of women in the vaginal birth group had their labours induced or augmented, something that midwives experienced in breech birth would rarely, if ever, recommend. Time limits were applied to the vaginal birth group – a classic example of the confounding variable of the clock as technology. More babies in the vaginal birth group acquired infections – but then prophylactic antibiotics were given to the caesarean group, so the infection rates of babies not given this advantage were bound to be higher by comparison. The researchers managed to completely ignore the possible impact of issues like mobilisation and maternal position during labour and birth and the environment of birth in general. In short, the study tells us absolutely nothing about the relative outcomes of vaginal breech birth where women are giving birth (as opposed to being delivered), and leaves us with a gap in our knowledge.” (Wickham 2003).

I was not alone

I was not alone in my concern.

The concern was international, and although the authors tried to defend their work, many people now believe the results of this trial to be of little value. 

However, the trial and its aftermath significantly impacted guidelines, and midwives’ and obstetricians’ skills in vaginal breech birth, although some independent midwives and a few hardy obstetricians and midwives working within the system in different countries continued to attend breech births throughout this time.  

Here are a few of the other commentaries which criticised and critiqued this trial.

Canadian Term Breech Trial Resources

• Maggie Banks’ Commentary on the Term Breech Trial was one of the first critiques
• Andrew Kotasta’s excellent 2004 article in the BMJ has been cited many times
• An example of the midwifery discussions on breech birth
• Marek Glezerman wrote a ‘five years on’ paper for AJOG
• Debates also go on in journal correspondance
• A 2010 paper by Betty-Anne Daviss et al on the responses to the Trial
• A 2015 discussion in the BJM
• A ‘ten years on’ review by Gerald Lawson in Birth in 2012
• A 2012 article by Henry Murray, which includes many points about the methodological failings of the study
• A 2017 list of key research published since the term breech trial (Rixa Freeze, posted in 2017)

Wickham S (2003). National breech rescue? TPM 6(3):38.

photo credit: paul bica via photopin cc

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