I have been promising workshop participants throughout this spring that I will write a blog post about the 35/39 trial, whose results were published just before I went on the road. Now that I’m back, I’ve managed to put my thoughts together, and here they are…
If you’ve not heard of the 35/39 trial, it was designed to evaluate the effect of early induction of labour – at 39 weeks – in older women (aged 35 or over) having their first baby. And yes, let’s start by acknowledging that 35 isn’t that old, and 39 weeks is relatively early to induce labour, especially given that methods of dating pregnancy aren’t that accurate. With induction of labour, there’s always a chance that we’ll get it wrong and bring about the birth of a baby who is younger than we thought.
So why do such a study? Well, because some people think that this might be a way of reducing the stillbirth rate, although it should also be noted that plenty of other people don’t think that early induction for older women will make any difference. There is lots of concern that early induction will cause more problems than it solves and create more inecessary intervention. In some ways, the paper published from the study seems to be trying to reassure people about that last issue – that early induction of labour in these women will lead to more intervention – but we’ll come to that in time.
One of the most striking things about this study is that it had incredibly low recruitment levels. Women over 35, it would seem, do not want to have their labours induced at 39 weeks, and I can’t say I blame them! The authors acknowledge that 86 per cent of the women who were eligible to be included in the study declined to participate. In fact, only 619 women were randomised out of the several thousand who were invited to participate, and the trial was thus underpowered to consider whether early induction makes a difference to stillbirth rates. The published paper states that the primary outcome was caesarean delivery, although secondary outcomes considered neonatal wellbeing.
The findings? “There were no maternal or infant deaths and no significant between-group differences in the women’s experience of childbirth or in the frequency of adverse maternal or neonatal outcomes”. (Walker et al 2016: 813)
So let’s be clear: no babies were worse off because their mums waited to go into labour naturally, and early induction of labour conferred no advantage to women or babies.
When they analysed their results using intention to treat analysis, the researchers also found that there was no significant difference between the caesarean section rates in the two groups of women. This has been the case with other papers looking at induction and caesarean section and I believe that we should be a bit careful not to take this result at face value. This finding is counter to the experiences of many people who work on labour wards and may well be due to professional factors. That is, some clinicians may be more likely to consciously or subconsciously recommend caesarean section in the groups of women who are in spontaneous labour at a later stage of pregnancy than that at which they think induction should have taken place.
The authors stress that there was also no difference between the two groups in relation to the women’s experience of childbirth. However, there are a few things to take into account here, and it is worth noting that this finding is contrary to the results of a recent study showing that women who experienced induction of labour reported negative experiences. We mustn’t forget that the women who reported their experienced in the 35/39 trial were only the 12% of women who didn’t mind whether their labour was induced or started spontaneously, so they are quite a specific group. (I’m sure they are lovely women; this is no criticism of them … I’m just saying that they may not be representative of all women).
It would be interesting to explore the feelings and experiences of some the 86% of women who didn’t want to be in the trial, although I’m saying that because I think it’s always important to look at the bigger picture and I do realise that this wasn’t possible in this situation. But other issues come into play here as well. We know that women often feel one way immediately after their birth – when they are generally really happy that they’ve come through the journey and that they and their baby are healthy – and sometimes feel differently as time goes by. I’m not saying this happens to every woman, but it’s an issue. Researchers also know that there is a tendency for people to assume that the care they received was the best possible care, and maternal satisfaction surveys are not always good measures of the quality of care.
So we should perhaps be a little sceptical about the suggestion that early induction in older women makes difference to the caesarean section rate or to women’s experiences, as these are not hard outcomes and there is reason to question both.
With no benefit to early induction in older women then, does that mean that we can hope that the recommendation for early induction, which is increasingly made where women are having their first baby later than average, will be abandoned?
Sadly, I doubt it, although I would love to be wrong. The authors of this study conclude by stressing that early induction of labor in older women doesn’t affect the caesarean section rate and isn’t associated with adverse short-term effects on maternal or neonatal outcomes. Rather than drawing the obvious conclusion that this practice therefore has no demonstrable benefit, the authors of this study instead argue that their results “provide support for the safety of performing a larger trial to test the effects of induction on stillbirth and uncommon adverse neonatal outcomes in women 35 years of age or older, although such a trial would need to be extremely large”. (Walker et al 2016: 821)
As far as whether another run of this unpopular trial gets off the ground is concerned, we will simply have to wait and see. But that shouldn’t stop us sharing these results with women, families and colleagues and letting them know that the results show no benefit to early induction in older women.
Walker KF, Bugg GJ, Macpherson M et al (2016). Randomized trial of labor induction in women 35 years of age or older. NEJM 374(9): 813-22.
A version of this blog post appeared in the March edition of my Birth Information Update. If you’d like a free monthly update of recent birth-related news, research and thinking and to be among the first to hear about my new projects, click here to sign up.
photo credit: Kalender / calendar via photopin (license) and Body Painting via photopin (license)
If you’d like to learn more about post-term pregnancy and build your confidence with the evidence, I’d love to welcome you to my online course on this topic 😀 And you can keep up with my research postings via my free updates and monthly Birth Information Update.