Women of all sizes have successful pregnancies and give birth to healthy children, so why then is Body Mass Index (BMI) a condition when it comes to in vitro fertilisation (IVF)? Among many medical bodies, there is a consensus that there is an ideal BMI for fertility* and IVF.

The complicated relationship between weight and fertility is taken one step further when it comes to fertility treatment through the NHS, which operates different rules between different Integrated Care Boards, so, depending on where you live, access to NHS funded fertility treatment is a postcode lottery.

Being told that your BMI is too high, whether you’re trying for NHS or private fertility treatment, makes what is already an emotionally and physically demanding journey feel even more complicated, frustrating and isolating. If you’ve experienced that situation or are concerned about what effect your BMI might have on your fertility and access to IVF treatment, read on.

Introduction to Fertility Treatment

Fertility treatment is a complex and highly personalised process that involves various medical interventions to help individuals or couples conceive. Understanding the relationship between BMI and fertility can help individuals make informed decisions about their reproductive health.

What is BMI?

Body Mass Index is a widely used measurement to assess an individual’s weight relative to their height. It is calculated by dividing the person’s weight in kilograms by the square of their height in metres and is categorised into several ranges, including underweight, normal weight, overweight, and obese.

For fertility treatment, and according to the NHS, a healthy BMI range is typically considered to be between 19 and 25. Being underweight or overweight can lead to irregular menstrual cycles, ovulation issues, and reduced fertility. It is essential to maintain a healthy BMI to optimise fertility outcomes and minimise potential risks associated with fertility treatments.

•       Under 19 is considered underweight

•       19-24 is considered normal

•       25-29 is considered overweight

•       Over 30 is considered obese

The NHS has a handy tool to help you calculate your BMI based on your height and weight.

It is important to note that BMI may not accurately reflect body fat in muscular individuals, such as athletes, due to their higher muscle density.

What is the role of BMI in fertility treatment?

In fertility settings, BMI is often used as part of the eligibility criteria for accessing NHS-funded IVF treatment in the UK. Across many NHS trusts, the BMI limit for female patients to access IVF is between 19 and 30, although some clinics accept up to 35. For male partners, some clinics also set BMI thresholds, typically under 35, but policies vary widely. While private clinics may have more flexibility, BMI-related considerations may still influence medical advice.

Women preparing for pregnancy, especially those with a higher BMI, are often advised to take 5mg of folic acid daily for at least one month prior to conception.

Why BMI Matters in IVF, according to the guidelines

There are no limits based on BMI for fertility treatment in UK law. However, NICE (National Institute for Health and Care Excellence) guidelines currently recommend that a woman’s BMI should ideally be below 30. This is based on research suggesting:

  • Higher BMI may reduce success rates for IVF due to hormonal imbalances, reduced ovarian response, and lower embryo implantation rates.
  • Pregnancy risks may be higher, including gestational diabetes, pre-eclampsia, miscarriage, and complications during delivery. A BMI of 30 or more is associated with a higher risk of pregnancy complications for both the mother and baby.
  • Anaesthetic risk during egg collection procedures is also cited as a safety concern.

But these guidelines are not without controversy, and for many individuals, being turned away or delayed from IVF treatment because of their BMI feels deeply unfair, particularly when many women with a higher BMI are successfully conceiving and delivering healthy babies naturally.

How can your BMI affect your chances of successful IVF?

There is some research** to suggest women with increased BMI have worse IVF outcomes than women with a normal BMI, namely, higher cycle cancellation rates, fewer harvested oocytes, fewer available embryos, and lower LBRs, as the body responds less effectively to fertility drugs.

Furthermore, studies have found a distinct correlation between higher BMI and lower live birth rates and a higher rate of miscarriage, often due to fewer eggs being produced during IVF.

A high BMI, specifically over 30, is often linked to lower egg quality and higher risks of implantation failure. Excess body fat can also cause hormonal imbalances and ovulation issues, reducing the likelihood of conception. There are also concerns over how extra weight can lead to conditions like gestational diabetes, preeclampsia and hypertension.

Low BMI and Fertility Treatment

It’s not just being overweight that can affect your chances of IVF success; being underweight can pose challenges too, impacting the likelihood of a successful pregnancy.

Those with a BMI below 19 are in danger of hormonal imbalances that could lead to irregular menstrual cycles, poor egg quality and insufficient endometrial lining development, which is crucial for implantation.

A low BMI can also lead to inadequate fuel for the body, making it challenging to support a healthy pregnancy. Fertility clinics often recommend that women with a low BMI gain a healthy amount of weight to optimise their fertility outcomes.

A balanced diet and regular exercise can help individuals with a low BMI achieve a healthy weight and improve their overall health. It is essential to work with a fertility clinic to develop a personalised plan to address low BMI and fertility treatment.

The Emotional Impact of Being Told “No”

For many people, being told their BMI is too high for IVF adds another layer of trauma to an already challenging journey. Common emotions include:

  • Shame or embarrassment around body image
  • Frustration with inflexible policies that don’t consider the full picture
  • Grief or loss at delayed or denied access to treatment
  • Isolation, particularly when others appear to access treatment more easily

It’s important to acknowledge that these reactions are valid. No one should feel they have to “earn” their way into being worthy of parenthood. It’s important to recognise that various health conditions, such as hormonal disorders like PCOS, can influence BMI and should be considered when evaluating eligibility for IVF.

What are my options if I’ve been told my BMI is too high for IVF?

If you’ve been told your BMI is too high for IVF, there are several things you can do:

For those with a high BMI, focusing on gradual and sustainable weight loss through a balanced diet and regular exercise can improve overall health and increase the chances of successful IVF.

Explore Second Opinions or Different Clinics

Not all clinics use the same criteria. Some NHS trusts have more flexible policies, and private clinics may be able to offer IVF regardless of BMI, though they may still advise on risks and success rates. Exploring different clinics can also provide access to various assisted conception methods that may be more accommodating to individuals with higher BMI.

Consider a Holistic Health Review

Rather than focusing solely on BMI, ask for a full health assessment, including:

  • Blood pressure
  • Blood glucose (for diabetes risk)
  • Hormonal panel
  • Thyroid function

This can give a more accurate picture of your fertility and pregnancy risks. A holistic health review considers many factors, including hormonal balance, overall health, and lifestyle, to provide a more accurate picture of fertility and pregnancy risks.

Work with a specialist fertility dietitian or GP

If you are aiming to reduce BMI, focus on sustainable, health-focused changes rather than extreme dieting. You’ll likely find better success by working with professionals who understand fertility and don’t promote shame-based approaches. Working with a specialist can help in making lifestyle changes that are sustainable and health-focused, improving fertility outcomes.

Make some lifestyle changes

There are a number of lifestyle changes that anyone embarking on an IVF journey should look at making, regardless of their BMI, but for those with a high BMI, should have an additional impact.

  • Maintain a healthy diet: Focus on consuming nutrient-dense foods like vegetables, fruits, lean proteins, and whole grains while reducing the intake of processed foods high in fats and sugars.
  • Limit alcohol and caffeine consumption: Alcohol contains a lot of calories, and excessive alcohol intake can impair fertility.
  • Exercise regularly: You don’t have to bust a gut down the gym, but engaging in moderate activities like brisk walking, swimming, or cycling can help you manage your weight effectively, boost your fitness levels, reduce stress and improve general wellbeing – all factors which can improve fertility!

Losing or gaining weight through a combination of healthy eating and regular exercise can significantly improve fertility and overall health, making it an essential part of preparing for IVF.

Being told your BMI is too high for IVF can feel like a devastating setback, but it’s not the end of the road. Whether you’re pursuing lifestyle changes, exploring private care, or simply seeking emotional support, there are ways forward.

*https://reproductive-health-journal.biomedcentral.com/articles/10.1186/s12978-022-01558-9

**https://pmc.ncbi.nlm.nih.gov/articles/PMC7884488/