In the U.S., nearly 100,000 babies were born through assisted reproductive technology, such as in vitro fertilization, in 2021, and as people postpone parenthood to older ages, such technologies are growing in demand.
IVF has the potential to realize the dreams of many would-be parents, but thousands of women of reproductive age in the U.S. may face barriers to accessing treatment — sometimes, even before setting foot in a fertility clinic.
These women all have something in common: They have a body mass index that categorizes them as obese or severely obese. BMI is calculated via a formula that takes height and weight into account, with BMIs between 18.5 and 25 considered to be a "healthy weight."
Most clinics in the U.S. exclude women with a high BMI from accessing IVF because of concerns that the procedure may be too medically risky, and that IVF treatment will be less effective in higher weight individuals. The cut-offs are not consistent across clinics but broadly can be between 35 and 45. And such guidelines are not unique to the U.S.: Around the world, BMI restrictions limit women's access to IVF treatment.
Despite the widespread exclusion, critics have argued that these restrictions are not medically or ethically justified.
First, we must acknowledge that IVF can be challenging for everyone, and less than half of embryo transfers result in a live birth — a success rate that lowers dramatically with age. Yes, IVF success is lower for higher weight women, but it doesn't have a substantially different success rate. Analysis of a quarter million IVF cycles in North America found that live birth rates in women categorized as normal weight (BMI between 18.5 and 25) were 31.4%, compared with live birth rates of 26.3% for women classified with class 2 obesity (BMI between 35 and 40).
Denying the opportunity for pregnancy based on an imprecise proxy for health is simply unfair because it systematically removes the reproductive choices of an entire a group of people.
Furthermore, although research has shown a slightly higher risk of minor complications during IVF egg-retrieval, serious complications were uncommon in women with a high BMI, according to one 2019 study.
Whether elevated risks justify outright denial of treatment is a pertinent question. Philosophers and ethicists have urged us to think about it another way: Pregnancy is a stressful, risky, and taxing bodily process for women of all weights. There is always the possibility that things could go wrong, and denying the opportunity for pregnancy based on an imprecise proxy for health is simply unfair because it systematically removes the reproductive choices of an entire a group of people.
A multitude of social, structural, and medical factors demonstrate that BMI limits are discriminatory. In a 2022 article, obstetrician-gynecologist Breonna Slocum and colleagues discuss how women from racially and socially marginalized communities are more likely to meet the criteria for obesity and by default be excluded from IVF.
BMI is now being criticized as an inappropriate measure for people of color as it was developed using data primarily collected from previous generations of non-Hispanic White populations.
BMI restrictions also do not often consider the impact of health conditions affecting weight such as polycystic ovary syndrome, or PCOS. Women with PCOS are likely to struggle with both fertility and losing weight. And we should question why systems regulate women's bodies so much without much thought for the male partner or sperm donor.
When researching IVF clinic policies, I noticed a striking absence of restrictions regarding male characteristics such as weight, age, and lifestyle, even though IVF outcomes are negatively influenced by sperm DNA damage.
In reality, women try desperately to lose weight in order to qualify for treatment. And if women can improve their health through weight loss, shouldn't they at least try? Weight loss before fertility treatment may not be helpful or even possible for most women. Most IVF clinics also have age limits, and egg reserves that get depleted over time mean weight loss could simply take too long to be worth it.
A recent review of clinical controlled trials found that weight loss achieved through structured dieting and exercise programs prior to IVF did not appear to improve live birth rates. The authors conclude that it is difficult to even assess these interventions as many people regain weight quickly. This "yo-yo dieting" stresses the cardiometabolic system and can increase the risk for diabetes, leading to worse health in the long term.
Quick-fix weight-loss medications also need to be carefully investigated before being offered as an option to women. Richard Legro, a professor of obstetrics and gynecology at Penn State College of Medicine, led a randomized trial on lifestyle interventions before IVF. In an interview, he told me that new weight-loss drugs such as retatrutide have potential to help women lose weight, but these medications can be more expensive than fertility treatment itself, and companies are cautious about potential risks to the developing fetus.
As BMI restrictions differ by geographical area and clinic ... there is a blurry, subjective line between those deemed too outside the norm and those who are just acceptably thin enough to receive treatment.
Why, despite the lack of medical evidence, do BMI limits on IVF persist, and why are clinics so reluctant to allow women in larger bodies to access IVF?
Health care decision-making is as much a messy social practice as it is a cold cost-benefit analysis. Research on health care rationing has found that emotional intuition can influence whether a patient receives treatment or not. Practitioner and policymaker decision-making can be based on irrational judgments as much as objective evidence because we all hold underlying morals, values, and feelings about what is right.
There is also tension between those who view obesity as a medical problem and others who understand "fatness" to be a socially constructed identity. While there is a dominant narrative in medicine that obesity is a lifestyle disease, critics argue that our ideas of health are shaped not only by medical evidence but also by our cultural preference for thinness.
Western societies tend to hold the view that obesity is an unhealthy personal choice and a moral failing. As a result, negative attitudes and beliefs about body size can affect health care decision-making.
Experimental studies on weight prejudice have found that powerful negative feelings for people in larger bodies can affect their treatment in everyday life, and research has shown that weight bias persists in medical settings. These so-called moral emotions may shape how we interpret the evidence in front of us. We need to question whether it is fair to make people jump through hoops of social approval just to access the same fertility care as everyone else.
Policies do not explicitly acknowledge the cultural discourses shaping our views. And as BMI restrictions differ by geographical area and clinic — even within the same country — there is a blurry, subjective line between those deemed too outside the norm and those who are just acceptably thin enough to receive treatment.
The women seeking fertility care who fall victim to these arbitrary boundaries are being silenced by systems that do not consider a patient's autonomy, their ability to lose weight healthily, or their personal risk profile. This needs to change.
In 2021, the American Society for Reproductive Medicine Practice Committee recommended that a process of shared decision-making should guide larger patients' access to IVF treatment. Currently, clinics give too much weight to shaky evidence and snap one-sided judgments.
Becca Muir is a Ph.D. candidate at Queen Mary University of London researching fertility care access. She has written for outlets such as New Scientist, The Guardian, Prospect magazine, and elsewhere.
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