Induction of labour at or before 42 weeks of pregnancy: new evidence

Another study has added to our knowledge about induction of labour at or before 42 weeks of pregnancy.

This topic has been in the news probably more than any other pregnancy and childbirth related issue in recent months.

I have also spent a lot of time debunking and challenging some of the spin that has been put on this issue.

The latest study has been published by Rydahl et al (2019), and their study shows that the evidence isn’t nearly as clear-cut as some people and organisations would like us to believe.

Their paper is freely available and describes a cohort study based on data from women in Denmark (Rydahl et al 2019).

They looked at what happened before and after the recommended timing of induction of labour was changed from 42 weeks of pregnancy to 41+3 weeks of pregnancy.

Rydahl et al (2019) looked at lots of outcomes and compared what happened during the two time periods in which the different induction of labour protocols (or recommendations) were in place.

What did they find?

The researchers found that there were no differences in stillbirths, perinatal deaths or low Apgar scores, which are considered to be the most important short-term, physical outcomes.

However, in the time period in which women were offered earlier induction, there were more inductions (which one would expect) and women experienced more interventions. Not just those which are part of the induction process, but other kinds as well. This isn’t new or particularly surprising; we know that intervention tends to lead to more intervention.

In Rydahl et al’s (2019) study, earlier induction of labour was also associated with an increase in uterine ruptures. The rate went from 2.6 per thousand to 4.2 per thousand.

Again, this is not entirely surprising. Induction of labour often involves the use of powerful drugs which stimulate the uterus to contract, and these can sometimes stimulate the uterus too much. But this finding is worrying, and serves as a reminder that induction of labour is associated with possible risks and negative consequences as well as possible benefits.

So what do the findings tell us about induction of labour at or before 42 weeks?

The findings of this study show that there was no advantage to bringing the nationally recommended induction date forward from 42 weeks to 41+3 weeks (Rydahl et al 2019).

This will be a moot point in many areas of the world, as induction of labour is already recommended before 42 weeks weeks. But this data is still quite important right now, not least because of a Swedish study which recently made media headlines when it was stopped because of concerns about stillbirth. The fact that the Danish data shows that stillbirth rates did not differ between 41+3 and 42 weeks is significant for women’s decision making. It highlights the very uncertain nature of our knowledge in this area and the fact that there are more factors to take into account than population-level data which is not considered in the context of the individuals concerned.

Some people and organisations are calling for earlier and earlier induction, either as a population-level policy or in certain groups of women who are deemed to be at higher risk (often without good evidence that induction of labour will do anything to lessen the chance of a problem).

But it is clear that there is more to this picture than they would have people believe.

Earlier research

An earlier review of trials comparing induction of labour with expectant management also concluded that evidence is lacking for the recommendation to induce labour at 41 weeks instead of 42 weeks for the improvement of perinatal outcome (Keulen et al 2018).

This is an important review and reminder, especially in the wake of recent studies looking at even earlier induction of labour. 

Keulen et al (2018) highlight some important points arising from their systematic review of 22 trials, including the fact that the risk of perinatal mortality between 41 and 42 weeks is low, there is no difference in caesarean section rate between induction at 41 or 42 weeks of pregnancy and is it thus unclear whether it would be better to recommend induction at 41 or 42 weeks.

Expectant management, for anyone who doesn’t know, describes what happens where we await spontaneous labour while keeping an eye on things in case earlier intervention is warranted.

Expectant management isn’t about saying an absolute ‘no’ to induction of labour; it’s the decision to ‘wait and see’; to tailor care to the needs of the individual woman and baby. No matter what the research says, of course, the decision is the woman’s, and the goal is to help women make the decision that is right for them.

Diving into the research issues

One important issue that the authors of this review discuss is the methodological (or research design) problems that have to be overcome and taken into account when we are looking at the outcomes of studies and reviews on induction of labour and other birth-related interventions.

Research studies aren’t carried out in a vacuum; they happen in the real world and are affected by human factors. It is very clear to those who design, carry out, use and appraise research that, sometimes, we see certain results or outcomes not because there is a clear difference between two courses of action in reality, or because one course of action is actually superior, but because the research design or something else that was going on at the same time either unwittingly or intentionally biased the outcomes.

A good example of this is where studies show that induction of labour reduces the caesarean section rate. Many people who work on birth suites say that their reality is that induction of labour frequently leads to other interventions, and deeper analysis of reviews on this area also raises many questions, because the decision to do a caesarean section is a human one and not a hard outcome measure. 

Henci Goer has illustrated some of these issues really well in her analysis of the recent ARRIVE trial, Harvard professor Neal Shah also contributed to the conversation about how such trials can be biased. and ‘Why ARRIVE should not thrive in Australia’ was published in Woman and Birth. More recently, I spotted this article in Midwifery Today on the same topic and this one from Sarah Buckley.

Keulen et al (2018) have provided a really useful discussion of some of the issues that are debatable, and which may be interpreted differently by different researchers and reviewers.

Their work further confirms that it isn’t good enough to simply cite a research study as evidence that a particular intervention is associated with a particular outcome.

We need to dig deeper, think hard about the absolute and the relative risk of different options and carefully consider what was happening behind the scenes of these studies which might have affected the outcomes.

That’s not because researchers are sloppy, uncaring or determined to reach a particular conclusion. It’s because research is carried out in our complex, messy, human world, which contains loads of factors that can affect the outcomes and leads us to need to engage our brains when thinking about whether the results are relevant to us and those we serve.

Where do we go from here?

If you would like to know more about induction of labour, I have a whole page of resources on this website and a book which helps explain the issues and the evidence.

We need more than this, though.It is also really clear to me that we need to do more to help women and families understand this topic and the evidence that relates to it. 

Rydahl E, Declerq E, Juhl M et al (2019). Routine induction in late-term pregnancies: follow-up of a Danish induction of labour paradigm. BMJ Open 9:12. https://bmjopen.bmj.com/content/9/12/e032815

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