Cervical dilation is (now mathematically shown to be) unpredictable

The unpredictable cervix

The idea that cervical dilation is unpredictable will not come as a shock to most people who read my books or blog. This is a key theme in my upcoming book.

And many people don’t need research to confirm their experiences.

But I think it’s important to share the findings of studies which add weight to midwifery knowledge and/or progress our thinking about everyday areas, so it’s in that vein that I offer this blog post.

I’m not going to repeat everything I’ve written in my book. There is an entire section called ‘At Your Own Pace’, which looks at issues relating to labour progress. But this will give you a taster…

Dilation is unpredictable

Back in 2015, a team of researchers in Italy confirmed, using some genuinely clever maths, that in spontaneous, naturally progressing labour, the rate of cervical dilatation is largely unpredictable.

That was the headline then, and it still is now.

Except we’ve had almost a decade of further research since then and it says very much the same thing.

More evidence, the same results…

A large 2018 study in the BJOG, involving almost 10,000 women across thirteen hospitals in Nigeria and Uganda, looked specifically at whether cervical dilatation over time could predict which women would go on to experience severe adverse outcomes.

The researchers concluded that “labour is an extremely variable phenomenon, and that dilatation over time is a poor predictor of adverse outcomes” (Sousa et al 2018). They suggested the one centimetre an hour myth needs re-evaluating.

Then, in 2023, a systematic review in the American Journal of Obstetrics & Gynecology tried to draw together the evidence from all the labour curve studies published since Friedman’s original work in the 1950s.

This proved somewhat difficult.

What’s the problem?

The problem for researchers like He et al (2023) is that, even among the studies that specifically looked at acceleration and deceleration phases of labour, researchers can’t agree on when these phases even begin.

Some placed the acceleration phase between 2 and 4cm, others between 4 and 5cm, others 5 to 6cm.

The researchers concluded that, “…there is an emerging consensus that the definition of abnormal labor may not be related to an idealized or average labor curve.” (He et al 2023).

It’s not the maths

A 2024 scoping review pulled in over a hundred studies on labour curves and arrived at much the same place: we still have no single reliable model which maps how dilation progresses.

While some researchers argue that we just need better maths, this isn;t the logical conclusion from the data itself.

The data strongly suggest that there IS no one model.

That variation itself is normal. (This is something I discuss more in my upcoming book).

An unchanging picture

So the picture hasn’t changed; it’s just got more evidence behind it.

Women who are left to their own devices will labour at their own pace, and variation is normal.

Some women labour faster, some slower.

Sometimes this varies in response to what’s going on around them.

Sometimes labour will pause.

And generally quite unpredictably.

The value of research

It can be good to have studies to back up this kind of knowledge, and not just because we live in a world that seems to demand scientific proof of everything, regardless of whether that’s the best way of investigating everything we want to know.

However, watching scientists try to measure and predict the rate of cervical dilation in labour is a bit like watching a cat chase the beam of light from a torch someone’s shining on the wall. Utterly pointless fun for a bit, but not something you’d want to spend all day doing.

And not much fun at all for the women involved, some of whom are asked to undergo even more vaginal examinations than usual so that enough data can be gathered.

But what can we do with this knowledge?

I differ slightly from the researchers on what we do with this knowledge.

The Italian team in the first study I mentioned above suggested that future research should focus on diagnosing the causes behind apparently erratic cervical changes.

I’m still not convinced that diagnosis is a necessary feature of a normal, physiological process.

And, again, I think the body of research on this topic clearly indicates that there are no simple, linear relationships waiting to be uncovered here, however good the maths gets.

So how about we redirect some of that research funding into teaching more people to watch and respect? Maybe even to be patient?

There’s a reason I mention the value of knitting in my book. And it’s not because I think it’s possible in modern maternity care. I’m well aware that it isn’t. I mention it as a reminder of what we’ve lost, and of what we could create if we could follow the science and the evidence.

It would make a nice change from the constant measuring, meddling and messing about with what is a normal and healthy part of women’s lives.

And, as the evidence keeps confirming, a thoroughly unpredictable one too.

For more information

I’ve just written a long book about midwifery knowledge, in which I share my view that all kinds of knowledge can be useful, as long as we are willing to be discerning and subject it all to scrutiny. In it, there is an entire section on labour progress.

 

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