The Motherhood Diaries: BMI & Babies, Pt 3 – The Expert Opinion. Is Weight In Pregnancy The Risk Factor We’ve Been Lead To Believe?

In part three of our Babies & BMI special, we talk to four experts – a nutritionist, an obstetrician, a fertility doctor and a midwife – about where the BMI really is important, and where they would like to see the system changed when it comes to a hyper-focus on weight in pregnancy.

Welcome to our series, The Motherhood Diaries – a safe space for you to share your experiences, advice, hopes and heartbreaks. We’ll be hearing from industry experts giving practical advice alongside Capsule readers (You!) sharing your firsthand experiences. We’re looking at everything from fertilitytrying to conceivepregnancythe fourth trimester, newborns, toddlers, children’s mental health and teenagers, fertility issues and everything in between! 

One of the things that first struck me when it comes to this topic – be it with my own experience, or in interviewing others – was how inconsistent the treatment of weight in pregnancy was. Some people were weighed every single appointment and their treatment – either emotional, or medical – was entirely dependent on the number on those scales.

Some people were never weighed in their pregnancy, at all. Some gained ‘too much’ weight, some didn’t gain enough. The importance of the BMI as a medical marker is already a squirrely kind of thing to prove, add in the shadowlands of pregnancy and it’s even harder to pin down. So I decided to speak to four experts – a nutritionist, an obstetrician, a fertility doctor and a midwife to get their broad range of opinions on this complicated, infuriating and necessary health marker.

BMI In Theory vs BMI in Practice

When Annaliese Jones was studying for her Bachelor of Health Science over 20 years ago, she was taught as part of her training that weight was a key factor in people’s health – and she was taught to use BMI as part of that.

The BMI, which stands for Body Mass Index, is the very simple equation of a person’s weight in kilograms divided by the square of height in metres. That information is then used to slot the individual into different weight categories – underweight, normal, overweight, obese, morbidly obese.

Now working in the field of nutrition, naturopathy and herbal medicine, Annaliese says the reliance on BMI as a health measure is very contradictory to the concept behind naturopathy – treat the individual, not the disease. And the lived experience of working in her field for two decades means that Annaliese has found that the importance of weight – and the reliance of BMI as a health indicator – just doesn’t stack up.

“In my opinion and experience, I have never actually seen weight be an issue for a client as far as getting pregnant or carrying a child,” she says. “I’ve never seen it impact negatively.”

The BMI is many things – and we’ll get into its complex origins later on – but one thing it is, is convenient. The World Health Organisation officially adopted the BMI measure as standard practice in 1995, and it has since become – globally – the accepted metric for categorising patients by their weight.

“It has become super ingrained into different institutions now – including public health institutions, where they need a way to categorise who can and can’t receive certain surgeries or procedures, or fertility treatments,” Annaliese says. “I understand that – because there can be more complications [with higher BMI] – but every case should be taken on the individual. We know better – in all different areas of health, we do know better. But we’re still not doing better by our patients.”

This mentality is mirrored by Dr Andrew Murray, Group Medical Director of the Wellington team of Fertility Associates. To get funded IVF in Aotearoa, currently, you have to have a BMI of 32 or less. This number, Andrew says, was put in place over 20 years ago, by the Ministry of Health. “At the time, there was evidence that success rates with IVF were certainly lower if your BMI was 32 or higher, and that the probability of complications in pregnancy was going to be higher.”

However, in that 20 years, the success rate for fertility treatment in general has increased for everyone. “As a result, there are perfectly good success rates for women with a BMI up to around 35 – and potentially beyond,” Andrew says. The care from the obstetrics and midwifery departments has mirrored this success rate. “Because people are just getting bigger, we’re getting better at looking after those people,” he says.

‘What many of us are now arguing is that the current BMI restriction does discriminate against certain ethnicities.’

One of the biggest controversies of the BMI is that it makes absolutely no allowance for how different ethnicities have different body compositions or different amounts of body fat.

“What many of us are now arguing is that the current restriction of the BMI of 32 does discriminate against certain ethnicities, who in general have a higher BMI,” Andrew says. “Something like 40% of Māori or Pasifika women have a BMI of above 35, so by default, it’s making it even harder for those women who already have trouble access funding for fertility treatment.”

In the last month, Fertility Associates has put together a submission for the Ministry of Health, focused on the issue of BMI. “We very much want to address the inequities that are apparent in the health system, particularly for Māori and Pasifika women,” he says. “And we think the current BMI cut-off is creating an inequity. If that restriction can be lifted to 35, we feel that will help improve access for many Māori and Pasifika women.”

The BMI Is Based On A Very Limited Study

When you consider the global importance of the BMI as a health measure, its origin story is frankly quite farcical. It was invented in the 1830s by a Belgian statistician, sociologist, astronomer and mathematician, called Lambert Adolphe Jacques Quetelet. He produced the study – based on the bodies of French and Scottish men – to roughly work out ‘the average man’ and explicitly said it should be used on a population level, rather than on an individual basis (sorry we let you down, Adolphe).

It gets worse – please read this excellent article The Bizarre and Racist History of the BMI by Aubrey Gordon and listen to the BMI episode of her outstanding podcast Maintenance Phase for more information – but basically, not only does the BMI have murky morals, it’s also not very good science.

“If I’d known the science back when they were teaching us the BMI at university – and how old it is, and the fact that it was developed using white middle class people – I think if people knew that about the BMI when they were learning it, when they were being told to use it as a parameter, I think people would question it a lot more,” Annaliese Jones, naturopath and nutritionist, says.

As well as not having any flexibility for ethnicity, the BMI also has other huge limitations. “It doesn’t tell us composition of the weight component – whether it’s muscle, bone, or fat,” says Dr Andrew Murray, Fertility Associates Medical Director. “We know that an excess of abdominal fat – the fat that sits around our internal organs – is unhealthy and in the fertility space, we also know that both men and women have their fertility affected by having too much abdominal fat.”

There’s a correlation, he says, between that kind of fat and an increase of inflammation, which can damage the eggs and the sperm. “So BMI is one very indirect way of getting an understanding of what someone’s internal body fat might be.”

The BMI Is Not Always A Good Measure Of Health

For Dr Kira Brent, obstetrician and specialist at National Women’s Health, the BMI is great for looking at overall data trends, but can be very limited when it comes to looking at individual health.

“You could be a really fit and healthy BMI 32, or you could live on a diet of pretty terrible food and have a BMI of 24,” she says. “Frankly, the really healthy BMI 32 might actually have better pregnancy outcomes than the poorly nourished BMI 24. So for the individual, the BMI is of less importance but for the data, it is really important – and I don’t know how to get around it. We do need those markers to be able to compare populations.”

A study, published in the International Journal of Obesity in 2016, looked at more than 40,000 participants and found that almost half of those with BMIs in the overweight range – and 29% of those in the obese range – were considered metabolically healthy. On the other side, more than 30% of those in the ‘normal’ range where considered metabolically unhealthy. Known as ‘the obesity paradox’, there are multiple studies that back up this idea that an active overweight person has a higher overall quality of health than an inactive thin person.

When it comes to the issue of weight and her patients, Dr Kira says she chooses to focus on the full wellness picture. She’s clear to point out that a higher weight does increase the risk of diabetes, gestational hypertension and pre-eclampsia, among other risk factors, but that the nuances of the individual’s health are also important.

“If a woman has a BMI of 60, she is higher risk in many respects and as an obstetrician, my job to safely deliver her baby is influenced by that BMI – there is a point where BMI is quite important,” she says. “But the nuances are also important. Honestly, I would rather see a fit, healthy woman with a BMI of 32, than a woman who had had a BMI of 32, and has crash-dieted her body to a BMI of 31.”

Your BMI Has An Impact On Your Options, Geographically

Manya Lynch, a midwife, also agrees that the BMI is not helpful on an individual level, but plays a big part when it comes to the variation of care that different health centres can offer. “You understand why it’s important but also, I’ve worked with bigger women – and I’m talking women who have BMIs in the 70s – are showing me that they just get on and have babies, without any issue whatsoever,” she says.

But there are absolutely risks and difficulties that can come with a patient who is in that BMI range – bigger babies, smaller babies; not to mention a higher risk of serious comorbidities like high-blood pressure and diabetes, and things can be a lot harder to monitor due to excess weight during the pregnancy. And as a midwife who has worked in both rural and urban settings, Manya knows first-hand that a patient’s BMI affects the logistics of birth in other ways – including where they can give birth, due to the range of different resources available at different clinics.

Because of the three tiers that make up our health system – primary, secondary and tertiary care – there are BMI restrictions on some clinics and hospitals, due to the resources available. This can affect a pregnant person’s options in terms of what’s available to them in their area – and what is available to the midwife, in her working area as well. These restrictions can be as much about the safety of the mother and baby as they can also be about the comfort of the mother – the higher the BMI, the more there might be need for appropriate equipment, and a wider range of options of things go wrong. “It’s all about the ‘What if,’” Manya says. “It’s not because something is going to happen, it’s about the ‘what if’ something happens.”

“From the perspective of the midwife or clinician, you’ve got protocols that you’re bound by due to the clinic you’re working at. Even when you’re talking to the woman initially, over the phone at the booking stage, you’re having to ask them their height and weight, so you know you can provide the appropriate care for them, in the location where you (the midwife) work  – or where she wants to birth,” Manya says. It’s also important to remember that midwifery is a consistently under-resourced and under-staffed area that is always in high demand – and this affects what’s available where, as well.

“It’s not as simple as ‘I can’t look after you, because you’re too big,’ it’s the decisions you’re having to make, as the practitioner, about having to split your time between different parts of the city. It becomes about the logistics, not the woman. It’s not personal.”

Judgement Around Weight Makes Things Worse For Everyone

“Weight is hugely emotional, because it’s hugely personal,” says Manya. “Nobody needs to tell you if you’re overweight; you know if you’re overweight. It’s because of the comorbidities that go with weight that the conversations need to happen and we have a responsibility, professionally, to deliver certain information – whether it’s about those heightened risks, or about increased monitoring throughout the pregnancy. But it’s all in the delivery of it, that’s what I’ve learned.”

So much of being a midwife, Manya says, is having to have difficult conversations, in an informative and non-judgemental way. “It’s important to have those difficult conversations, so that you’re giving the mother all the information that she needs,” she says. “But there’s nothing worse than having a really difficult conversation where the mother feels a thousand times worse than when she came into that situation. Because that’s the trauma. So we can have those conversations in a gentle way.”

‘There’s nothing worse than having a conversation where the mother feels a thousand times worse than when she came into that situation. Because that’s the trauma.’

This fits with Dr Kira Brent’s approach as well, in her role as an obstetrician. “If someone comes to see me and they happen to have a weight that’s in the obese range, then they have a weight that’s in the obese range,” she says. “Shaming women, making them feel insecure or inadequate about their body at a time when it is changing significantly anyway, is not okay. But working with a woman to make lifestyle changes that can mitigate risk can be a very positive approach, with benefits that I hope might extend beyond pregnancy.”

Kira says she is aware that, in her own private practice, she “goes rogue” when it comes to not monitoring a patient’s weight every time they come in for an appointment. “The New Zealand maternity schedule recommends that we should weigh you every time you come in; it’s a part of routine antenatal care,” she says. “While I have not found any convincing evidence that ‘weigh-ins’ at every appointment have been shown to have any benefits, I’m still very mindful of how I can monitor for the risks associated with weight in a way that is empowering, compassionate and women-focused.”

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