We Need to Rethink BMI Requirements for Egg Freezing and Donation
Body Mass Index (BMI) is a measure that has been used for decades to put people into the weight categories of “underweight”, “normal weight”, “overweight”, or “obese”. While it is often used as an indicator of a person's overall health, BMI has been increasingly criticized by medical experts as a flawed and unreliable measure.
This is particularly true in the context of fertility clinics, where someone’s BMI can determine if they are eligible for egg freezing or donation. Some clinics have set a BMI threshold, which means that women who are considered overweight or obese are often turned away from services without a fair look at their full health.
It’s time to reconsider these antiquated policies which are based on flawed assumptions, and move to an evidence-based care model that is tailored to each individual's unique needs and circumstances. Let’s dive in.
What is BMI?
BMI stands for Body Mass Index, which is a numerical value calculated from a person's weight and height. It is commonly used as a measure of body fat and as an indicator of overall health. The formula for calculating BMI is weight in kilograms divided by height in meters squared.
BMI has been widely used by medical professionals as a quick way to assess a person's overall health and risk of various health conditions, such as heart disease, diabetes, and certain cancers. However, the accuracy of BMI as a measure of body fat and health has been questioned in recent years, and many experts argue that it is a flawed measure that should be abandoned.
The problematic history of BMI
The history of BMI is linked to eugenics, a pseudoscientific movement that gained popularity in the late 19th and early 20th centuries. Eugenicists believed that some races and ethnicities were inherently superior to others, and sought to promote the reproduction of "desirable" traits while discouraging or even preventing the reproduction of "undesirable" traits.
One of the key figures in the development of BMI was Adolphe Quetelet, a Belgian mathematician who was also a proponent of eugenics. Note that Quetelet was not a physician, nor did he work in medicine. His work on BMI was influenced by his belief that different races and ethnicities had different ideal body types, with northern Europeans being the most "perfect." As a result, he believed that BMI could be used to identify individuals who deviated from this ideal.
Quetelet's work on BMI was later adopted by the life insurance industry in the early 20th century, as a way to calculate the risk of insuring different individuals. This led to the widespread use of BMI as a measure of obesity, despite its questionable scientific validity.
This racist history of BMI (as recognized by the American Medical Association) is an important reminder that the use of BMI as a measure of health is not only scientifically flawed, but also rooted in deeply problematic beliefs about race and ethnicity. It is time for us to move away from this outdated and harmful measure, and to adopt more inclusive and accurate measures of health and well-being.
How BMI cut-offs for egg freezing perpetuate reproductive health inequities
We know that Black and Latina women are more likely to face infertility than white women, yet face more obstacles when it comes to receiving fertility care.
Adding a hard BMI cut-off for access to egg freezing without holistically evaluating someone’s health further perpetuates this inequity. That’s because the prevalence of “obesity” (according to BMI) is higher among Black and Hispanic women, making them disproportionately impacted by BMI requirements.
Why BMI is medically flawed
Not only is the BMI calculation primarily based on white body types and not always an appropriate measure for people of other races or ethnicities, but medically it’s flawed.
One major flaw is that BMI does not distinguish excess fat, muscle, or bone mass. This means it is inaccurate in certain populations such as athletes (who have a lot of muscle mass) or those who are very tall or very short.
“The body-mass index that you count on to assess obesity is a bizarre measure. We live in a three-dimensional world, yet the BMI is defined as weight divided by height squared. It was invented in the 1840s, before calculators, when a formula had to be very simple to be usable. As a consequence of this ill-founded definition, millions of short people think they are thinner than they are, and millions of tall people think they are fatter.
- Nick Trefethen, Professor of Numerical Analysis, University of Oxford in a letter to The Economist, 5 January 2013
For example, a perfectly healthy bodybuilder who is 6 feet tall and weighs over 185 pounds would be considered overweight. If their weight was over 220 pounds, they would be considered obese, even if this individual had a very low body fat percentage and was in excellent physical health. Conversely, someone with a low muscle mass and high body fat percentage could have a "normal" BMI but still be at risk for health problems.
Also, BMI does not provide any indication of the distribution of fat in the body. The location of body fat is an important variable in assessing the metabolic as well as mortality consequences of excessive fat accumulation.
Relying solely on BMI to assess health is an unfair shortcut that can lead to bias and potentially harmful outcomes.
BMI and egg freezing: what does the data actually say?
The truth is, there is insufficient data on the effects of BMI and egg freezing outcomes. And at the time of writing this, I could find no studies on BMI and egg donation, since women with BMIs over 30 have largely been shut out of the opportunity to donate their eggs.
Here’s what we do know:
BMI and egg yield
The evidence of the effects of high BMI on IVF outcomes is conflicting and inconclusive. One review from Washington University in St. Louis looked at egg retrieval outcomes and obesity. They found eight studies that reported lower numbers of eggs retrieved, and nine that found no difference.
However, these studies are from infertile IVF patients and not fertile egg freezing patients, and as such the correlation to egg yield cannot necessarily be extrapolated from one population to the other.
There is one study I could find on BMI and egg freezing (373 elective egg freezing cycles). The study found that egg yield actually increased by 2% per increase of BMI measured, and that BMI was a significant predictor of eggs retrieved when controlling for confounding variables. However, the majority of women in their cohort had a “normal” BMI and only nine had a BMI over 29 (considered “obese”). Regardless, the authors conclude that in the context of egg freezing, patient demographics are dissimilar to the IVF population.
BMI and egg quality
There’s insufficient and conflicting evidence on the effect of BMI on egg quality.
The same Washington University in St. Louis article referenced above looked at the effects of obesity on egg quality. They found:
Egg quality: six studies found an adverse effect, one found no effect
Fertilization rates: three studies found decreased rates, eight found no difference
Embryo quality: two found decreased quality, two found no difference
Again, though, these studies are in infertile populations and can’t necessarily be extrapolated to egg freezers. Plus, fertilization rates and embryo quality have unrelated confounding factors like sperm quality.
BMI and procedure complications
Can obesity lead to more procedure complications? There’s not a lot of data on this, but one study of 1,947 egg retrievals found that while patients with a BMI over 40 were more likely to require higher doses of propofol and fentanyl, the retrievals were able to be safely performed.
Some people claim that BMI can cause complications under general anesthesia, which is typically used in the egg retrieval process. However, clinics are finding ways to safely perform the procedure under local anesthesia, eliminating many risk factors.
BMI and overall health
As mentioned above, BMI as a metric evaluated in isolation does not provide an accurate picture of one’s overall health. It does not consider other factors such as the body composition or distribution of body fat, as well as blood pressure, cholesterol levels, medical history, or other markers of health. Additionally, BMI can be influenced by factors outside an individual’s control, such as genetics, age, and ethnicity. One study on the correlation between BMI and cardiovascular health found that having a ‘normal’ BMI did not guarantee good cardiovascular health and having an above ‘normal’ BMI did not guarantee poor cardiovascular health. The researchers took many other health indicators into account, such as blood pressure, cholesterol, triglycerides, blood sugar, and the c-reactive protein (marker for inflammation).
BMI and egg donation
Nowhere in the Food and Drug Administration (FDA) or American Society for Reproductive Medicine (ASRM) guidance for egg donation is BMI mentioned. Regardless, many clinics set an egg donor threshold of a BMI of 30.
Recently, ASRM voted to adopt a new AMA policy urging doctors to limit the use of BMI as a sole identifier of overall health and obesity. The policy states that “there are significant limitations associated with widespread use of BMI in clinical settings and suggests its use be in conjunction with other valid measures of risk.”
BMI thresholds act as a disservice to intended parents looking to grow their families, and disproportionately affects intended parents of color, who already face greater difficulties finding donors of their same race.
It’s time to abolish the BMI disqualifier for egg freezing and donation
BMI, as a single measure, should not disqualify someone from egg freezing or donation. I’m not suggesting that clinics ignore the health of patients – but rather that they look at their health more holistically. While weight and height should be considered as part of the overall evaluation process, it should not be used as a sole criteria by clinics for disqualifying women from egg freezing or donation.
In an ASRM committee opinion on obesity and reproduction, ASRM directly states: “Obesity should not be the sole criteria for denying a patient or couple access to infertility treatment.” So why do we allow it to be a disqualifier for egg freezing and donation?
By denying women access to egg freezing services based on their weight alone, clinics are essentially denying them the opportunity to preserve their fertility and their reproductive autonomy. Egg freezing may be even more important for people with high BMI, who are statistically more likely to struggle with infertility down the road. This can have devastating consequences for women who may want to delay pregnancy for personal or medical reasons, such as cancer treatment.
Moreover, the focus on BMI as a measure of health ignores the many other factors that can impact a person's fertility, such as age, genetics, lifestyle, and medical history. By fixating on BMI, we are are oversimplifying a complex issue and perpetuating harmful stereotypes about weight and health.
It is time for all fertility clinics to stop using BMI as an immediate disqualifier for egg freezing and donation. Instead, they should focus on providing evidence-based care that is tailored to each individual's unique needs and circumstances.
In a world where medical science continually refines its understanding of human physiology, clinging to outdated metrics like BMI as a gatekeeper for reproductive freedom is not merely archaic—it's a negation of evidence-based care. When it comes to the right to preserve fertility, the dimensions of the scale should never outweigh the nuances of individual health and autonomy.
Disclaimer: I am the Cofounder and Chair of Cofertility, a platform that empowers women to take control of their fertility timelines by making egg freezing more accessible. Our Split program enables women to freeze their eggs for free when they donate half of the eggs retrieved to a family who can’t otherwise conceive including LGBTQ+ parents, couples facing infertility, and those with other fertility-impacting medical challenges, like cancer.
Since we work with clinics across the country, we have to follow their screening guidelines, including cut-offs for BMI. More and more clinics— like Nova IVF— are moving towards evidence-based evaluation for health beyond BMI, and I hope this trend continues.
This article is my opinion alone and does not represent that of Cofertility.