Weight and IVF: a sensitive topic, clear data

Patients have told me they were turned away by a clinic without explanation, or, conversely, that they never heard a word about weight until after a third failed attempt. Neither approach is satisfactory. Here is what we know.

Body Mass Index

BMI is calculated by dividing weight (in kg) by the square of height (in m). A value between 18.5 and 25 is considered normal; between 25 and 30, overweight; above 30, obese; and below 18.5, underweight. It is an imperfect tool — it does not distinguish between muscle and fat — but it is the one used by studies and clinics.

The effects of a high BMI

• Ovulation: excess adipose tissue disrupts hormonal balance, particularly in cases of PCOS.
• Stimulation: higher doses of gonadotropins are often required.
• Egg retrieval and embryo transfer: technically more difficult, with more delicate sedation.
• Outcomes: large meta-analyses show a moderate decrease in birth rates above a BMI of 30, and more miscarriages.
• Pregnancy: increased risk of gestational diabetes, hypertension, pre-eclampsia and caesarean section.

It is interesting to note that in egg donation, the effect of the recipient’s BMI on implantation is weaker: part of the effect is therefore attributable to egg quality. The risks associated with pregnancy, however, remain.

Centre thresholds

There is no legal BMI limit in Greece. Each clinic, and above all each anaesthetist, sets its own rules. Many accept a BMI of up to 35, some accept higher figures with precautions; others require prior weight loss. Ask about this when you first make contact, giving your weight and height, to avoid any unpleasant surprises.

Losing weight before IVF: is it helpful?

A weight loss of 5 to 10 per cent may be enough to restore ovulation, and sometimes to enable a spontaneous pregnancy. However, trials that have delayed IVF to impose a weight-loss programme have not always resulted in more births in the end: time lost matters, especially after the age of 35. The balance therefore depends on age and ovarian reserve.

What works best: a Mediterranean-style diet, regular and moderate physical activity, and sufficient sleep. Highly restrictive diets are not recommended during the period leading up to conception. Medicines in the GLP-1 agonist class (such as semaglutide) must be stopped before conception, generally at least two months beforehand, in accordance with medical advice.

Bariatric surgery is sometimes considered in cases of severe obesity; in such cases, pregnancy is generally not recommended for the following 12 to 18 months.

Being underweight too

A BMI below 18.5, restrictive dieting or very intense exercise can block ovulation (hypothalamic amenorrhoea). Gaining weight is often sufficient to restore cycles. The risks of preterm birth and low birth weight are also higher.

And what about men?

Male obesity is associated with reduced sperm concentration and motility, as well as increased DNA fragmentation. Weight loss, giving up smoking and cutting down on alcohol often improve the semen analysis within three months.

A word on how to discuss this

Weight is neither a fault nor a moral matter. It is one medical factor amongst others, such as age or thyroid function. If a doctor broaches the subject in a hurtful way, you have the right to say so and to find another doctor. If no doctor raises the issue even though your BMI is over 30, you also have the right to ask about it. See also diet and supplements.

Frequently asked questions