Liz Fox was 34 when she started fertility treatments. Languishing on a long waiting list for NHS-funded IVF, she and her husband decided to go to a private clinic. There was still a delay, however: Fox was told her body mass index (BMI) was too high.
“My BMI was above 35. They said, you need to be at most 35 to be eligible for treatment with us,” she tells Spotlight. Fox wasn’t deterred. “I started exercising and discovered that I really enjoyed it, and I went to went to see a nutritionist, so started eating a lot better,” she recalls. By the time she began treatment, “I think my BMI was 33. I was in a good place, both physically and mentally.”
BMI – an equation in which a person’s weight, in kilos, is divided by the square of their height in metres – is routinely used by the NHS as a standard measure of health and well-being. But patients with a high BMI often complain of being dismissed by doctors, with health problems blamed on their weight. “If you’ve got a bad toe, it’s because you’re fat,” says Fox. “If you break your leg, it’s because you’re fat and you fell over.”
Fox’s first round of IVF, paid for privately, failed, so the couple moved onto the NHS, where a consultant told them rules set out by their local Clinical Commissioning Group (CCG), the regional organisations that determine which NHS treatments are funded in each area, meant that Fox’s BMI was still considered too high. This time it had to be below 30.
Conscious her age was now creeping towards another limit set by the CCG – 40 is usually the cut-off for accessing treament – Fox became desperate and put herself on a 500-calorie-a-day diet. The diet, a quarter of the daily calorie intake recommended for women by the NHS, made her light-headed and irritable and gave her stomach cramps. “I had to stop exercising,” she says, but “my aim was to become eligible for NHS treatment. I just had tunnel vision to get to that goal.”
After weeks of being “miserable” on the diet, she achieved her goal – or so she thought. On the set of scales she used at home she calculated that her BMI was “29 point something”, but when she went for an assessment at her NHS clinic the scales used by the nurse put it at “30.1 or 30.2”. The nurse, Fox says, saw the “look of absolute devastation on my face, took pity on me and was like, ‘It’s fine, I’m sure we can just put it down as 30’.”
The evidence of how BMI affects IVF is not conclusive. Although studies have shown patients with a high BMI respond less well to fertility treatment – and that if they do conceive, a higher body weight can lead to gestational diabetes and premature birth – many problems that cause infertility in the first place, such as polycystic ovary syndrome (PCOS), cause sufferers to gain weight easily, and make losing it extremely difficult.
Fox is far from the only person to go to extreme lengths to access fertility treatment. Guidelines set out by the National Institute for Health and Care Excellence (Nice), which informs the treatments offered by the NHS, mean only those with a BMI between 19 and 30 qualify for treatment. Like Fox, those who fall outside this bracket often turn to crash diets or extreme exercise to qualify for treatment, which can cost tens of thousands of pounds at a private clinic.
BMI was originally created by a statistician, not a doctor, and was never intended as a measure of health. Adolphe Quetelet, a Belgian scientist and mathematician, sought a way to define “l’homme moyen”, the average man. He came up with his calculation, which suggested height and weight were directly proportionate. But Quetelet’s equation fails to account for differences in body composition. Someone can have a high BMI because of muscle mass, for instance. There are cases of more muscular people with high BMI who have eventually qualified for IVF treatment, but not before a lengthy, stressful appeal process. This can be very damaging: once they have begun fertility treatment, time is very rarely a luxury people have.
“The importance of BMI should be assessed on a case-by-case basis,” says Geeta Nargund, the medical director at Create Fertility, a private provider that has 16 clinics in the UK and one in Denmark. “It may well be that for older women or those with reduced egg reserve, a clinic decides that starting treatment earlier – if it is safe to do so – before waiting for the patient to reduce their BMI could be more effective.”
Critics of BMI point out that not only does it fail to account for differences in body composition, it also ignores the differences between men and women – and between ethnicities. Quetelet’s calculation was based on a sample of white, European men, they argue, and health systems’ dogged focus on it means people from other groups are prevented from accessing vital healthcare, including fertility treatment. Black and brown women are, for instance, more likely to suffer from PCOS.
Pragya Agarwal, a data scientist whose books (M)otherhood and Sway address some of these issues, is blunt about it. BMI “does not take diversity of bodies into account,” she says. “It perpetuates weight bias and discriminates in particular against women of colour. BMI cutoffs disproportionately affect historically marginalised populations and people of lower socioeconomic status. Reliance on BMI creates reproductive inequities. The definition of obesity is also contentious and we have to reflect on ‘obese by whose standards’ and how were these standards determined and when.”
In recent years the World Health Organisation has made one attempt to rectify this, suggesting different cut-off points for determining obesity in Asian populations because their health risks are different. Last year Nice released new guidelines that, among other things, indicated that for those from a “South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background… risk occurs at a lower BMI”. It added that BMI should be interpreted “with caution in adults with high muscle mass” and for those over 65.
In some cases, it suggested, waist-to-height ratio should be used. Others agree this is a better indicator of a person’s health: a study published in 2017 in the journal Plos One found that waist-to-height ratio could more accurately describe a person’s risk of obesity than BMI.
Agarwal points out that the opinion of the American Society of Reproductive Medicine is that “on the basis of available evidence, there is no medical or ethical directive for adopting a society-wide BMI threshold for offering fertility treatment; rather there is considerable evidence arguing against such a policy”. She says: “My research shows that even though there have been some studies that have shown the impact of weight on fertility and associated obstetrical risks, this has not been reliably proven or recommended to completely preclude women who are considered overweight from fertility treatments.”
For those who have been forced to lose weight to access treatment, the focus on BMI tends to leave a scar. Fox eventually conceived through a privately funded round of fertility treatment and had her baby in early 2022, but she won’t forget her experience. “Losing weight was such a trauma for me: it should be about exercising for health, exercising for well-being, looking after myself because I want to be there for my daughter until she’s as old as I am, minimum,” she says.
She also points out that, unlike in usual conception, the BMI rule takes the ultimate decision over whether to have a baby out of the hands of the very people affected by it, instead giving it to IVF’s gatekeepers. “It’s only the women that have to go through treatment in order to potentially have a baby who are scrutinised in that way,” she says. “I’m not stupid, I know there is going to be an effect on the outcome. But women of all shapes and sizes get pregnant.”
Emma Haslett is the co-host of the Big Fat Negative podcast, and co-author of the book of the same name.
This article is part of a series on the gender health gap. Click here for more in the series.