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Maybe you’ve just begun to explore egg freezing or donation and heard about Body Mass Index (BMI) as a clinical measure of eligibility for the procedures. Or perhaps you’ve already applied to donate your eggs and were told you did not qualify on the basis of BMI. Wherever you’re at on your egg freezing or donation journey, it’s possible that your BMI may come into question. You may be wondering what one has to do with the other, and if this criteria is even legit. 

BMI is a tool that categorizes intervals of body fat based on a person’s height and weight, with the associated categories being “underweight,” “normal weight,” and “obese.” Labels we really don’t love…but are used by the medical industry nonetheless. In the case of fertility clinics, BMI is often used as a requirement for egg freezing and donation. Most clinics have set a BMI threshold, meaning women considered overweight or underweight are often disqualified from receiving fertility services without any investigation into the rest of their medical profile. Because Cofertility is a matching platform and partners with fertility clinics, their guidance is what informs our policy. 

Let’s dive into BMI as a health metric, why some clinics rely on it for fertility treatment eligibility (the TLDR: correlating anesthesia risks), and why its roots can be problematic. 

A quick primer on BMI 

The formula for calculating BMI is weight in kilograms divided by height in meters squared.

It 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. Despite its imperfections as a metric (and the flaws of relying on any one measure to look at the big picture), historically, BMI has been used by the medical community to more easily identifying certain comorbidities.

Why fertility clinics take BMI into account

For better or for worse, fertility clinics — like other medical establishments — often look to BMI as one requirement when evaluating someone’s eligibility for egg freezing or donation. Here’s a bit more about the why.

What is the recommended BMI range for freezing or donating eggs?

First, let’s clarify what BMI requirements for egg freezing or donation even entail. They can vary by fertility clinic, but most criteria are based on CDC and WHO classifications of “normal weight.” At Freeze by Co, your BMI must be between 18-29 in order to qualify as a Split member — where you can freeze your eggs for free if you donate half of the eggs retrieved to another family who can’t conceive. If you feel like your BMI does not reflect your health, because you’re an athlete or otherwise, please send us a note. We also review lots of other health profile criteria as part of your application and understand that BMI is not always indicative of a person’s overall health.

If you’re a Keep member — where you can still freeze your eggs more affordably and keep 100% of them for your own future use — you may also be subject to similar BMI requirements as set out by clinic partners. It is worth noting that clinics’ BMI parameters for egg freezing may be more flexible than those for donation.

Does weight and BMI affect the retrieval cycle itself? 

It can. Probably the biggest reason fertility clinics are reluctant to conduct egg retrievals  on those outside the “normal” BMI range is that your BMI may affect your overall risk profile for the stimulation and procedure. Throughout the time that you are taking hormone stimulating meds, your doctor will monitor your ovaries through an ultrasound to measure follicle growth. Women with higher BMIs may have more abdominal tissue; thus, it can be harder for your doctor to visualize the ovaries and ensure that everything is progressing as expected. 

Further, the American Society of Anesthesiologists notes that a high BMI increases the risk of surgical and anesthetic complications. While some clinics are finding ways to safely perform the procedure under local anesthesia (eliminating many risk factors), fertility clinics don’t all necessarily have the same equipment you’d find at a hospital, and many are simply not comfortable with this risk for safety reasons. 

Women with very low BMIs may also be at risk of complications and side effects from ovarian stimulation, too. For example, some studies indicate that individuals with low BMI are at higher risk of developing Ovarian Hyperstimulation Syndrome (OHSS). 

According to Cofertility Medical Advisor, Dr. Meera Shah,"Research does suggest that obesity is associated with impaired fertility and decreased live birth outcomes with assisted reproductive technologies. Some studies have demonstrated a correlation with increased BMI and lower oocyte yield, mature eggs, and blastocyst development. Obesity may also increase procedural risks including anesthesia related complications and procedural complexity. From a clinical perspective, it is important to balance these risks with a woman's autonomy to preserve her fertility. It is important that this patient population seek extensive counseling regarding such risks and are referred to centers equipped with the resources to provide safe and compassionate care.”

Does weight and BMI affect egg retrieval outcomes? 

Maybe. A systematic review of 13 studies found that women with higher BMIs are less responsive to hormone stimulating medications. While these studies pertained to ovulation-inducing medications (like clomid) vs. medications specifically involved in egg freezing, it still indicated a potential need for higher total doses of follicle stimulating hormones for those with higher BMIs. 

Another large cohort study has shown that, relative to women of normal weight, overweight women (BMIs > 25) have fewer eggs retrieved per cycle. While we do have some data about the hormonal implications of very low BMIs — ASRM reports that very low BMIs can cause irregular menstrual cycles and may cause ovulation to stop altogether, impacting a woman’s fertility overall — evidence of the effects of low BMI on actual retrieval outcomes is more varied. We’ll continue to keep tabs on that data as it becomes available, but this heterogeneity may be due to smaller sample size of underweight groups or the influence of biological differences such as ethnicity (more on that below).

On the flipside, there is a single study on BMI and egg freezing (373 elective egg freezing cycles), which found that egg yield actually increased by 2% per increase of BMI measured. This study also illuminated the fact that the existing research on women with known infertility issues cannot be easily extrapolated to egg donors and freezers, because they are unique populations.

Does weight and BMI affect egg quality?

It can. Although there is not absolute consensus, some studies have shown that obese women can experience poorer egg quality. Because women are born with a limited number of eggs, the environment in which those eggs develop is critical. A study published in the Journal of Assisted Reproduction and Genetics stated that obesity impairs egg maturation. It can also induce elevations in insulin, glucose, or fatty free acids, all of which appear to impact the development of the egg. 

Another study done at Washington University in St. Louis looked at the effects of obesity on the egg quality of infertile women. They found:

• Oocyte quality: six studies found an adverse effect, one found no effect
• Fertilization: three studies found decreased rates, eight found no difference
• Embryo quality: two found decreased quality, two found no difference

As we review this study, though, we’ll need to remember that findings on infertile populations can’t necessarily be applied to egg freezers. Plus, fertilization and embryo quality have unrelated confounding factors like semen quality.

Why do you need a certain BMI in order to freeze or donate eggs? 

Most doctors set BMI parameters in response to data on outcomes and the complication risks shared above. In most cases, BMI limits are in place to protect your bodies and reduce the risk of complications. 

Also, when it comes to egg donation, specifically, since families needing egg donors have generally already been down a difficult, and expensive road, their doctors want to reduce any potential risks and increase chances of a successful retrieval. Given what you are putting your body through in order to stimulate and retrieve the eggs, this can be beneficial to all parties involved in the process. 

Why BMI can be a problematic metric

Clearly, there is a lot of contradictory research when it comes to BMI’s impact on fertility outcomes — our heads are spinning, too! Despite this, BMI is still widely used by fertility clinics to determine a woman’s eligibility for both freezing and donation. 

In recent years, more and more researchers and medical professionals have argued that BMI is a flawed method of body measurement. And while we need to comply with and respect the BMI parameters put in place by our clinic partners, we also have a few issues with BMI as a metric.

Looking at the full picture

As the Cleveland Clinic points out, BMI does not distinguish between 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. Similarly, BMI does not provide any indication of the distribution of fat in the body. And we know that the location of body fat in someone’s body is an important variable in assessing their full health picture.

Because the freezing and donation processes follow similar steps up until the point of retrieval, the fertility clinic you ultimately work with will likely ask you about your BMI as part of the Split and Keep programs. We want you to be prepared, and while there is a push for clinics to evaluate BMI as part of the full picture, for our Split program in particular we do need to ask about BMI on our initial intake questionnaire. Reason being: we would hate for someone to spend valuable time and energy on the program’s full application, only to be told by a fertility clinic that they would not qualify for egg donation based on this metric. 

Reliance on BMI can further perpetuate racial inequities

Relying solely on BMI to assess health also has the potential to lead to increased racial bias. Although the BMI calculation was primarily based on White body types and not necessarily an appropriate measure for people of other ethnicities, Black and Latina women are more likely to face infertility than white women, and may benefit the most from fertility preservation.

Yet, because of BMI cutoffs, these populations face more obstacles when it comes to receiving fertility care. The prevalence of obesity is higher for women of color due to myriad social determinants of health and differences in body composition. Therefore, women of color are disproportionately impacted by BMI requirements. Obesity prevalence in the U.S. in 2020:

• 39.6% of white women
• 45.7% of Hispanic women
• 57.9% of Black women

This doesn’t mean that the potential egg freezing risks associated with BMI described above should be disregarded, but we should acknowledge that this data does have the potential to perpetuate racial inequities. The AMA itself even states that it has “issues with using BMI as a measurement due to its historical harm, its use for racist exclusion, and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations.”

The need to preserve reproductive autonomy

If a clinic denies someone access to egg freezing services based on her weight alone, this essentially denies her the opportunity to preserve her fertility and her 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.

Insufficient data about BMI and egg donation

Ultimately, there is just insufficient data to make a conclusive assessment of the relationship between BMI and egg retrieval outcomes. And, when it comes to egg donation in particular, there are zero studies on the effects of BMI upon donation outcomes, since women with BMIs over 29 have largely been denied the opportunity to donate. 

So, how should we look at BMI?

The bottom line is that BMI evaluated in isolation does not provide an accurate picture of one’s overall health. And although we ask about our applicants’ BMI due to clinical compliance, we believe in improving accessibility to egg freezing for all. 

Despite being bound by clinical parameters for egg donation that we must screen for, we believe that BMI as a single measure should not disqualify someone from egg freezing or donation. Our hope is that fertility clinics instead consider patient health more holistically — in addition to taking BMI into account as one metric.

What industry governance *does* say

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.” Further, neither the Food and Drug Administration (FDA) nor the American Society for Reproductive Medicine (ASRM) provide specific guidance around the use of BMI. In fact, ASRM has recently voted to adopt the new AMA policy urging that “the use of BMI be in conjunction with other valid measures of risk.” 

Our hope is that fertility clinics consider these messages in assessing a patient’s overall profile. This could look like counseling and support for women who may be struggling with weight-related issues, or the exploration of alternative methods for assessing fertility, such as ovarian reserve testing. 

Moving forward, we hope that more fertility clinics focus on providing evidence-based care that is tailored to each individual’s unique needs and circumstances. One thing we can all agree on: the outcomes of holistic healthcare will always eclipse those grounded in the use of a single number. 

What are your options?

If you’ve been told you can’t move forward with egg freezing or donation due to your BMI, we know how disheartening this must feel. But this does not have to be the end of the road for you.  

If your BMI is above the appropriate range, available data suggests that as little as 5%-10% weight loss can improve fertility outcomes. Notably though, in order for weight loss to be most effective, it must be gradual and sustained. If your BMI is below the appropriate range, ASRM recommends working with your doctor to understand the cause of the situation and develop a plan to correct it. 

At Cofertility, our mission is to make egg freezing accessible, but we never want to compromise the health and safety of our members. If you’re interested in our Split or Keep programs but have concerns about your BMI impacting your eligibility, we recommend that you reach out to your doctor to discuss further. 

In addition, please don’t hesitate to reach out to us with any questions about our program qualifications. Even if you have to put your application on pause, we may still be able to help you get ahead of other requirements. And no matter what, we’ll be here for you as soon as you’re ready to move forward.