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

A lot has been written over the past few years about the risks posed to women with higher BMI than average.

In fact, this has become such a significant issue that I have written a book on this topic.

And, as I dug into the evidence, it became even clearer to me that the focus we place on BMI as a risk factor is problematic in a number of ways.

First, the additional tests, interventions and restrictions which are suggested when a woman has a higher BMI are often not supported by the evidence.

There is also wide individual variation that is missed when we focus in on single risk factors or measurements, such as BMI.

And focusing on BMI leads to weight stigma and disrespectful care, which are actively harming larger women.

Assumptions, bias, and distress

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. And these women’s concerns are warranted. Many studies show that the assumptions made about larger women aren’t evidence-based, and that the approach we’re currently taking isn’t the best that we could do.

For example..

Here’s just one of these studies, as an example. I hope that writing about it might help show that there is more that needs to be taken into account than tired, unevidenced assumptions about size.

The study is a population-based cohort study of characteristics associated with uncomplicated pregnancies in women with a higher BMI.

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 higher BMI without taking a risk-focused approach won’t be surprised to see the results.

That’s because, 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.

It is also clear that making assumptions and treating people differently because of how they look can lead to their having worse outcomes. There is evidence on this as well.

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 other people’s attitudes and beliefs about their size and shape.

I talk about this more in Plus Size Pregnancy: what the evidence really says about higher BMI and birth, and also in my 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).

Not a new finding

But these findings weren’t entirely new, even at the time.

A few years before, research published in BJOG: An International Journal of Obstetrics and Gynaecology had 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 (Hollowell et al 2014).

This was a study of 17,230 women without medical or obstetric risk factors. And the findings showed that, while the risk of interventions requiring obstetric care did tend to increase with BMI category, other things were going on as well. One was that parity – or whether the woman had had babies before – was actually much more important as a predictor of outcomes than BMI. Perhaps even more significantly for larger women, though, the increase in risk for women who are deemed to be overweight was actually far less than people had been saying.

Sadly, these findings made no difference to the way that larger women were being treated. If anything, the restrictions became more stringent. And the number of tests and interventions offered to women with a higher BMI have increased.

BMI is not a proxy for health

As I discuss in Plus Size Pregnancy, the evidence does not show a direct relationship between higher body weight or BMI and ill-health.

Having a higher BMI may be a risk factor for some people in some situations, but the issues are complex, both in maternity care, and in health care more widely.

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, and thus treat larger-bodied people differently.

These are just some of the reasons that explain why our current approach to women with a higher BMI isn’t helpful or evidence-based.

In fact, there is also evidence from a number of areas of health care that poorer outcomes may not be the result of someone’s body shape, but of the attitudes that others take towards them because of their body shape.

There is so much more to know about this topic. And those with a higher BMI deserve to know the facts.

I have written lots more about this in my book. I hope it will help you to better understand the evidence and make the decisions that are right for you.

References

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 DOI: 10.1111/1471-0528.12437.

Relph et al (2021). A population-based cohort study of characteristics associated with uncomplicated pregnancies in women with obesity. BMC P&C 21(182).

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


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