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You can be fat and fertile

Updated: Mar 14, 2023

Using an individual’s body mass index (BMI) as a measure of their general health is antiquated and inaccurate. We know that athletes who train every day and have very strict diets can have a BMI that states they are overweight or obese. And that many whose BMI categorises them as overweight or obese have an excellent bill of health and live an incredibly healthy lifestyle. So why then are we still using BMI cut offs to decide who is worthy of receiving fertility treatment?

Our reproductive system is controlled by a series of hormones. If there is an imbalance in these hormones we may face challenges with menstruation, ovulation, and our ability to conceive. Women in larger bodies (a BMI of over 30) are thought to be less fertile than women in smaller bodies due to the amount of fatty tissue present in larger bodies which may negatively impact the balance of hormones. There are also greater risks associated with being ‘fat’ and pregnant to both the mother and the baby (so previous research has claimed).

However, more and more articles are being written to challenge this school of thought and the supporting research. And, more importantly, questioning the moral principle of refusing a woman fertility support based on her BMI.

In the UK, fertility clinics have a cut off a BMI between 30-35kg/m2, meaning that you will not receive treatment until your BMI is below this level. A women’s general health is not taken into consideration, nor is her age. Which seems ridiculous because we know that the one thing that definitely affects fertility is a women’s age; the older we get, the more difficult it becomes to conceive.

The result of this unfair discrimination is that it leaves many women feeling unworthy of becoming a mother, women are delaying conceiving because they believe they need to be a certain weight before they can.

There is nothing quite like the desire to conceive and have children. Believe me when I say that many women will do whatever it takes to have the opportunity to carry and birth a child. So, when a woman is told that she needs to lose weight before she’s able to conceive you can bet your bottom dollar she will adopt any strategy to do so. This often means that women will severely restrict their calorie intake or eliminate whole food groups to drop the numbers on the scale. And do you know what happens when we don’t provide our body with enough nutrients and energy? It starts downregulating the systems that aren’t essential for survival – and yes, you guessed it, reproduction is one of these systems. So, by telling a woman she needs to lose weight, experts are potentially decreasing the chances of conceiving.

Woman looking at baby scan

Let’s look at what the studies say – or don’t say:

If we look at the studies which have concluded that women with higher BMI’s are less fertile you will notice that these studies have not accounted for age. They’ve lumped women of all ages into the same group. This is going to skew the results as the older we get the less fertile we become. We should be comparing women of similar ages as well as BMI.

Studies looking at how weight loss improves fertility are flawed for many reasons.

  • They cannot separate whether these women saw improvements in fertility because of the weight they lost or because of the lifestyle changes they made. It is not possible for us to see whether if they had made the lifestyle changes but remained the same weight, they would still see improvements in fertility.

  • As part of these weight loss programmes women often receive support that is unheard of in most weight management programmes, such as a weekly 3-hour session with healthcare professionals. Most women who are turned away from fertility clinics are left to their own devices and receive little or no support to help them lose weight. And as rates of overweight and obesity are higher in more deprived communities, these women usually don’t have the funding to seek support to lose weight safely.

Although these studies conclude that losing 5-10% of total body weight positively effects the ability to conceive and carry, for many this equates to only a few BMI points and it would not be enough to gain access to fertility treatments – despite studies telling us they would have improved their chances. That gets a mega eye roll from me!

Studies looking at the effectiveness of certain medications to help improve fertility such as Clomid (used to stimulate ovulation) indicate that these medications are less effective in women with a higher BMI. However, the doses given to all groups are often the same, regardless of weight or BMI. We know that certain medications need to be given in higher doses to those in larger bodies. We don’t give children and adults the same doses and any anesthetist will tell you that dosage is based on size.

In fact, a study where anovulatory women were treated with gonadotrophin to induce ovulation found that whilst women with a high BMI required higher doses of gonadotrophin, “there was no difference in the rates of ovulation and clinical pregnancy in relation to body weight.

A randomised control trial in the Netherlands (Mutsaerts et al., 2016) looked at the effect of lifestyle interventions prior to assisted reproductive technology (ART) versus immediate ART on the chances of live birth in obese sub fertile women. The lifestyle intervention did not result in more live born children than starting ART immediately, it actually decreased the number of vaginally delivered babies beyond 37 weeks. There were also no differences in pregnancy complications between the two groups.

There is in fact no evidence to support the BMI cut offs presented by fertility clinics. These cut offs are arbitrary numbers, potentially created to lighten the load on fertility clinics and save money in countries where fertility treatments are funded by the government.

Whilst no one is claiming that there is no risk during pregnancy and birth for women in larger bodies, it’s important to note that it’s not only women in larger bodies who carry these risks. Women with diabetes, similar to women in larger bodies, are at an increased risk for developing hypertension, congenital abnormalities, and premature labour, however they are not excluded from receiving fertility treatment.

Whilst I’m not saying that the risks should be ignored, patient centred care is about looking at the individual patient and not classifying/grouping them based on their BMI. It means taking a woman’s age into consideration as well as the damage that pursuing weight loss may have on her chances to conceive.


Balen, A., Platteau, P., Andersen, A., Devroey, P., Sørensen, P., Helmgaard, L. and Arce, J-C. (2006). The influence of body weight on response to ovulation induction with gonadotrophins in 335 women with World Health Organization group II anovulatory infertility. BJOG: An International Journal of Obstetrics & Gynaecology, 113(10), pp.1195–1202. doi:10.1111/j.1471-0528.2006.01034.x.

‌Banker, M., Sorathiya, D. and Shah, S. (2017). Effect of Body Mass Index on the Outcome of In-Vitro Fertilization/Intracytoplasmic Sperm Injection in Women. Journal of human reproductive sciences, [online] 10(1), pp.37–43. doi:10.4103/jhrs.JHRS_75_16.

Brown, R.C.H. (2019). Irresponsibly Infertile? Obesity, Efficiency, and Exclusion from Treatment. Health Care Analysis, 27(2), pp.61–76. doi:10.1007/s10728-019-00366-w.

Koning, A., Mol, B.W. and Dondorp, W. (2017). It is not justified to reject fertility treatment based on obesity. Human Reproduction Open, [online] 2017(2). doi:10.1093/hropen/hox009.

Mutsaerts, M. A., van Oers, A. M., Groen, H., Burggraaff, J. M., Kuchenbecker, W. K., Perquin, D. A., Koks, C. A., van Golde, R., Kaaijk, E. M., Schierbeek, J. M., Oosterhuis, G. J., Broekmans, F. J., Bemelmans, W. J., Lambalk, C. B., Verberg, M. F., van der Veen, F., Klijn, N. F., Mercelina, P. E., van Kasteren, Y. M., Nap, A. W., … Hoek, A. (2016). Randomized Trial of a Lifestyle Program in Obese Infertile Women. The New England journal of medicine, 374(20), 1942–1953.

‌Sathya, A., Balasubramanyam, S., Gupta, S. and Verma, T. (2010). Effect of body mass index on in vitro fertilization outcomes in women. Journal of Human Reproductive Sciences, 3(3), p.135. doi:10.4103/0974-1208.74155.

‌Slocum, B., Shami, A. and Schon, S.B. (2022). Body Size, Fertility, and Reproductive Justice: Examining the Complex Interplay between BMI, Reproductive Health, and Access to Care. Women, 2(2), pp.93–101. doi:10.3390/women2020011.


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