Labour progress myths: why size and age may not be the problem

A few years ago, two important papers from the Birthplace team helped us to unpack some labour progress myths.

They actually came out just days apart.

The impact of maternal obesity on intrapartum outcomes in otherwise low risk women: secondary analysis of the Birthplace national prospective cohort study, was published in print form in the BJOG (Hollowell et al 2014). I’ve also discussed that study in this blog post.

Then, just a few days later, The effect of maternal age and planned place of birth on intrapartum outcomes in healthy women with straightforward pregnancies: secondary analysis of the Birthplace national prospective cohort study (Li et al 2014) was published in BMJ Open.

Important research

These papers are important for lots of reasons. Here’s what I wrote at the time:

“I was particularly interested to read the latest paper because I have recently been thinking a lot about the issue of alleged poor uterine contractility in women who are larger and/or older than average.

I have also been discussing this with a number of other midwives, and I am particularly not as convinced as some of my esteemed colleagues that overweight women are intrinsically at risk from poor uterine contractility.

It’s just not what I (and apparently a good few of my colleagues) have seen in practice, sorry.

And yes, I know that what I’ve seen in practice is only my experience, but several aspects of national guidance relating to this area are based on the expert opinion of certain other practitioners, so I feel justified in throwing mine into the mix.”

Possibilities…

At the time, I went on to note that this is a complex issue and many possibilities exist, which are not necessarily mutually exclusive.

“Some possibilities to think about here include:

  • Some women have longer labours than others, and this is merely reflective of a normal range.  How boring it would be if every woman had the same labour!  If there are differences, is this actually a problem, or do we just need to adapt our thinking?
  • If there are differences, is it possible that these might be caused not by higher BMI and age per se, but by the differences in the environments in which we work, which (among many other elements) will include our perception of whether or not certain physical characteristics (such as age and size) are risk factors?
  • Could the kind of care – which might include, for instance, the degree of emphasis that the attendant places on the importance of creating a space that is more likely to enable women to release oxytocin – make a difference?
  • The mere act of labelling someone as ‘at risk’, let alone the increased monitoring which is offered to women who are perceived to be at increased risk, might – understandably – cause those women to feel anxious.  This might, in turn, make it harder for them to relax and release the oxytocin which promotes uterine contractility…

Sara looks at the evidence relating to higher BMI and birth, unpacking the myths and helping you understand your options.

It might well be that, for some reason that we have yet to uncover, women who weigh more or are older have poorer uterine contractility.  But this also might be iatrogenic and/or environmentally dependent.

It might be caused, in part, with the growing focus on so-called clinical complexity, and the effect that this has on practitioners’ expectations.

Or by size or weight bias, which we know is prevalent in maternity and health care.

As far as I can see, the theory of reduced uterine contractility is just one theory which isn’t evidence-based.

And more studies carried out in medicalised environments wouldn’t necessarily help, anyway. Especially when the labelling that exists in such environments is clearly part of the problem.”

In fact, my understanding of this area in relation to BMI has deepened, because I have since analysed the evidence relating to plus size pregnancy, in order to write a book on this topic.

I am even more certain that provider bias is a key issue when it comes to birth outcomes in plus size pregnancy, and this is confirmed by many other studies.

And I am confident that the same issue plays a part when it comes to birth outcomes and maternal age. As Li et al‘s (2014) findings showed (with emphasis in bold added by me), there is clearly a lot going on here that we don’t understand either:

“An age-related increase in augmentation is consistent with evidence of poorer uterine function at older ages,34 longer labours34 and an increased incidence of prolonged labour,35 ,36 but the reasons for a steeper increase in augmentation with age in non-OU [obstetric unit] settings are unclear.

It has been suggested that labelling of older women as ‘higher risk’ and/or heightened concern about the safety of older nulliparous women, particularly those who have required fertility treatment, may result in increased rates of caesarean section for non-medical reasons,20 ,32 ,33 ,37 and it is possible that similar factors affect midwives’ decision-making regarding transfer for failure to progress, or for other reasons.

Intrapartum transfers from midwifery units in the Birthplace study have been shown to increase significantly with age in nulliparous women29 and, once transferred, women are ‘exposed’ to the higher intervention rates found in OUs.”  (Li et al 2014).

It’s really clear that we need to stop attributing birth outcomes solely to women’s size, age, and/or race (or whatever other characteristic will become a so-called risk factor next) and recognise the part that fatphobia, agism, and racism play in outcomes.

Perhaps then more people will be able to see that these labour progress myths are just that – myths.

Hollowell J, Pillas D, Rowe R et al (2014). The impact of maternal obesity on intrapartum outcomes in otherwise low risk women: secondary analysis of the Birthplace national prospective cohort study. BJOG. 121(3): 343-55. 

Li Y, Townend J, Rowe R et al (2014). The effect of maternal age and planned place of birth on intrapartum outcomes in healthy women with straightforward pregnancies: secondary analysis of the Birthplace national prospective cohort study. BMJ Open 4(1): e004026. 

Wickham S (2023). Plus Size Pregnancy: what the evidence really says about higher BMI and birth. Avebury: Birthmoon Creations.


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