How Weight and BMI Affect Fertility
Body weight is one of the modifiable factors that can influence fertility, largely through its effect on hormone balance. Both excess weight and being significantly underweight can disturb ovulation.
This article gives an informational overview of how weight affects fertility in women and men, what body mass index actually measures, and how it is approached before treatment.
What is body mass index (BMI)?
BMI is a simple measure calculated by dividing weight by height squared. It broadly separates underweight, normal, overweight and obese ranges.
BMI is not a complete health measure on its own: it cannot distinguish muscle from fat, or where fat is distributed. It remains a practical starting point in a fertility assessment.
How does excess weight affect fertility?
Fat tissue is hormonally active and contributes to oestrogen production. A greater amount of it can shift hormone balance and disturb the regularity of ovulation.
Insulin resistance often accompanies excess weight. This is particularly relevant in polycystic ovary syndrome, where it can contribute to irregular ovulation.
Is being underweight also a risk?
Yes. Very low body weight and a low proportion of body fat can suppress the hormone signals travelling from the brain to the ovaries. Periods may become infrequent or stop altogether.
Intense exercise and restrictive eating can deepen this picture. See our article on ovulation and the fertile window for background.
Weight and male fertility
Excess weight can also affect hormone balance and sperm parameters in men, and raised temperature around the scrotum may contribute.
Lifestyle adjustments are considered alongside the semen assessment. See improving sperm count and quality for practical points.
The approach before treatment
When planning treatment, your doctor takes weight into account. The aim is not rapid weight loss but a sustainable, balanced pattern.
Sudden, highly restrictive diets can themselves disturb hormone balance. Our guide to nutrition and lifestyle covers a steadier approach.
Every situation is individual and planning should be done with your doctor.
Related Reading
- IVF Nutrition and Lifestyle: Before, During and After Transfer
- PCOS and Getting Pregnant: Symptoms, Diagnosis and Fertility Options
- Factors That Influence IVF Success
Sources and references
This article is supported by the following independent, authoritative sources: