BMI and fertility

Obesity

• women, and trans men and non-binary people with female reproductive organs who have a body mass index (BMI) of 30 kg/m2 or over, should be informed that:
  • that they are likely to take longer to conceive, and
  • that if they are not ovulating, losing weight is likely to increase their chance of conception
• women, and trans men and non-binary people with female reproductive organs should be informed that participating in a group programme involving exercise and dietary advice leads to more pregnancies than weight loss advice alone
• men, and trans women and non-binary people with male reproductive organs who have a BMI of 30 kg/m2 or over should be informed that they have an increased risk of reduced fertility

A review (12RCTs; n=1921) found moderate certainty that pre-IVF weight loss interventions were linked to increase in total pregnancy rates (risk ratio 1.21; 95% CI, 1.02 to 1.44) and pregnancies resulting from unassisted conception (1.47; 1.26 to 1.73) (2)

Notes:

• with respect to low body weight and fertility (1):
  • women, and trans men and non-binary people with female reproductive organs who have a BMI of less than 18.5 kg/m2 and who have irregular menstruation or are not menstruating should be advised that increasing body weight is likely to improve their chance of conception

Reference:

1. NICE (March 2026).Fertility - Assessment and treatment for people with fertility problems
2. Michalopoulou M et al. The Effect of Weight Loss Before In Vitro Fertilization on Reproductive Outcomes in Women With Obesity: A Systematic Review and Meta-analysis. Ann Intern Med.[Epub 12 August 2025].