Understanding BMI limits for fertility treatment

With fertility treatment, several factors can impact the chances of successful conception, one of which is your body mass index (BMI).

BMI is a way to determine whether you have a healthy weight for your height. If you are considering fertility treatment, it’s important to know the role that BMI plays in the process. Maintaining a healthy BMI is essential for fertility and can also make fertility treatment safer, particularly regarding anaesthesia during surgical procedures.

What is BMI?

BMI or body mass index, is a person’s weight relative to their height. It is calculated from your weight (in kilos) divided by the square of your height (in metres), giving a result in Kg/m2. It provides an estimate of an individual’s body fat and offers an insight into their health based on this calculation. For example. The higher the BMI, the more body fat is present, indicating lower healthiness.

It is classified into five categories:

Underweight: BMI under 18.5 Kg/m2.
Healthy weight: BMI between 18.5 and 24.9 Kg/m2.
Overweight: BMI between 25 and 29.9 Kg/m2.
Class I obesity: BMI between 30 and 34.9 Kg/m2.
Class II obesity: BMI between 35 and 39.9 Kg/m2.
Class III obesity: BMI 40 Kg/m2 or more

However, BMI calculation has its limitations as
muscle weighs more than fat. So muscular individuals may be inaccurately categorised as obese when they are not. Additionally, it is important to consider racial variations in BMI. For example, a healthy BMI range for an Asian individual would be classed as 18.5 – 22.9 Kg/m2.

How does BMI affect fertility?

BMI plays an essential role in both sperm and egg development, so being either underweight or overweight can significantly impact your chances of conceiving naturally. It can affect the effectiveness of fertility treatments and how the body responds to fertility medication. Additionally, a higher BMI may increase the risk of developing pregnancy complications such as diabetes.

Increasing obesity has a significant negative impact on fertility. An increased BMI makes egg retrieval more dangerous, both in terms of anaesthesia and increased risks of organ damage from the IVF needle. Additionally, it also has an impact on egg and sperm quality, resulting in poorer quality embryos and lower chances of implantation. For individuals with Class I obesity, the chances of implantation can decrease by 20-30% and this risk increases with a higher BMI. Furthermore, as fatty tissue produces oestrogen, this can interfere with the ovulation cycle and release of hormones, impacting growth, blood pressure and reproduction. Moreover, a high BMI can also increase the likelihood of complications during pregnancy, such as diabetes.

Equally, having a very low BMI can also have a negative impact on the frequency of ovulation and egg quality.

Why do BMI limits differ between NHS and private clinics?

The NHS only treats individuals with a BMI of 30 or less, while private clinics have their own eligibility criteria. The primary concern is the safety of patients undergoing surgical procedures that involve anaesthesia.

Patients with a high BMI may face complications during treatment, which is why the NHS and some clinics impose lower BMI limits. However, some anaesthetists at private clinics are more comfortable providing anaesthesia to patients with a higher BMI. Therefore, it is advisable to contact clinics directly to enquire about their specific BMI requirements.

What are the BMI guidelines for fertility treatment?

At TFP Fertility, we do our best to provide fertility treatment for a diverse range of individuals.

For patients undergoing in vitro fertilisation (IVF) treatment, ovarian stimulation and oocyte (egg) retrieval are required. Each clinic generally has an upper limit of 35 for body mass index.

This limit exists due to the technical challenges associated with the oocyte retrieval procedure in women with a higher BMI, as well as the associated risks during conscious sedation required for anaesthesia. In certain cases, we can treat women with a BMI of up to 37, but a special anaesthetic assessment would need to be carried out.

However, at TFP GCRM Fertility in Glasgow, our anaesthetists are comfortable managing patients with a BMI of up to 40 Kg/m². Nevertheless, it’s important to try to manage your weight as much as possible for all the reasons above.

Get in touch

Get in touch with TFP Fertility for fertility advice

For more information on our BMI requirements or fertility treatments, contact our patient team today to book your first consultation.

Speak to us 0808 120 3965