Women with higher BMI: it doesn’t have to be complicated!

We have heard much over the past few years about the risks posed to women with higher BMI than average. It’s clear, however, that this focus is problematic in a number of ways. The evidence isn’t clear cut. There is wide individual variation that is missed when we focus on single parameters. There is also much concern about weight stigma and disrespectful care.

Women with higher BMI have variously reported to us that they, “feel distressed after a call from a lifestyle midwife who spouted risks and then lectured me about causing harm to my baby,” are “sick of being patronised when I eat healthily and exercise every day,” and “just want someone to stop making assumptions based on one facet of my health when there is so much more to it than that.”

These quotes are just the tip of the iceberg. We receive many enquires on this topic and we’re unable to reply individually, However, I wrote about a recent study in my Birth Information Update that I think is worth everyone’s attention. It is my hope that writing about this here as well might at least help show that there is more that needs to be taken into account than tired, unevidenced assumptions about size.


A new study…

The study I spotted is a population-based cohort study of characteristics associated with uncomplicated pregnancies in women with obesity. Researchers in Canada set out, “to calculate the rate of an uncomplicated pregnancy (antenatal period) in pregnant women with obesity and to determine the demographic and clinical factors which are associated with such uncomplicated pregnancies. We also set out to determine if the prediction of uncomplicated pregnancy using identified factors is feasible amongst women with obesity.” (Relph et al 2021).

Those of us who already seek to give great care to women with a high BMI without taking a risk-focused approach won’t be surprised to see the results. When I talk to woman-centred practitioners who try hard to not treat people differently because of their size, I hear them express surprise at the idea that having a high BMI in itself leads to more problems. What is also very clear to those of us who are concerned about this issue (and there is some evidence on this as well) is that making assumptions and treating people differently because of how they look can lead to their having worse outcomes.

That means it’s difficult to untangle whether poorer outcomes and higher intervention rates are based just on size and shape, or whether (and to what extent) they are the result of people being treated differently because of their size and shape.

I talk about this more in my 2021 book, In Your Own Time: how western medicine controls the start of labour and why this needs to stop.


So what did they find?

In the case of this study:

“The study demonstrates that over half of women with obesity but no other pre-existing medical or early obstetric complicating factors, proceed through pregnancy without adverse obstetric complication.” (Relph et al 2021).

Importantly, the researchers argue that:

“Care in lower-risk settings can be considered as their outcomes appear similar to those reported for low-risk nulliparous women.” (Relph et al 2021).

Lastly, the research team have a suggestion for future research:

“Further research and predictive tools are needed to inform stratification of women with obesity.” (Relph et al 2021).


Stratify, or individualise?

I don’t know if I’m as convinced about that bit. I’d personally rather see an individualised approach, and there are other statements in the study that I don’t wholly agree with, but that’s often the case. This is a start towards a more woman-centred approach, and it’s always good to see more research exploring the notion that health isn’t based on one parameter.

More on this in In Your Own Time.

Not a new finding

But this isn’t an entirely new finding. A few years ago, research published in BJOG: An International Journal of Obstetrics and Gynaecology showed that women with a high BMI who have previously had at least one baby were less likely to experience obstetric complications during labour and birth than had been thought.

The results of this study of 17,230 women without medical or obstetric risk factors showed that, while the risk of interventions requiring obstetric care tended to increase with BMI category, parity was actually much more important as a predictor of absolute risk and the increase in risk for women who are deemed overweight is far more modest than is generally held to be the case.

One element of the findings is particularly worthy of reflection:

[T]he frequency of augmentation of labour suggests that failure to progress may have been the presenting problem in the majority (up to three quarters) of the cases where healthy obese and very obese women experienced outcomes that required obstetric care. This is consistent with a body of evidence indicating that obese women have less effective uterine contractility and longer labours, are more likely to experience failure to progress/labour arrest and have an increased risk of non-elective section for labour arrest disorders or ‘failure to progress / cephalopelvic disproportion’.  (Hollowell et al 2013: 10).

I know that I (amongst many other people) have said it before, but there is no direct relationship between higher body weight and ill-health. Having a higher BMI may be a risk factor for some people in some situations, but the issues are complex. It is also impossible to separate out the degree to which having a higher BMI is a risk factor because it truly leads to physiological differences from the degree to which it is a risk factor because people – whether women, clinicians or others – think it is a risk factor.

If you have a moment to spare, please read the quote above again.  The one about women ‘failing to progress’.

To what extent might clinicians’ perceptions that women with a higher BMI have less effective uterine contractility, longer labours and a greater likelihood of need for obstetric intervention create a self-fulfilling prophecy?



Who determines the outcome?

The ‘need’ for augmentation and/or cesarean section is not generally determined by a ‘hard’ measure, such as the woman’s blood pressure reaching a certain threshold. It is generally a subjective decision, and no such decisions are made in a vacuum. They are, instead, made in a context which includes and takes into account relevant factors and issues which may be physical, emotional, sociocultural, epistemological, environmental and/or systemic. They might, for instance, relate to the availability of staff, equipment and facilities.

Or attitudes.

This context also includes the cultural beliefs of the time, which today include the notion that women with a higher BMI are more likely to have problems. So it is not hard to see how the higher intervention rates experienced by these women may be caused by the fact that we think they are more likely to need intervention.

Which is why it is so helpful to see the authors of this paper recommending a more individualised approach, and suggesting that ‘it may be reasonable to review the BMI criteria for planned birth in non-obstetric unit settings‘ (Hollowell et al 2013: 11).

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