Body Mass Index (BMI)
Body Mass Index (BMI) is a numerical index calculated by dividing weight in kilograms by height in meters squared (kg/m²), used as a population-level screening tool for weight-related health risk. The World Health Organization classifies BMI below 18.5 as underweight, 18.5 to 24.9 as normal range, 25.0 to 29.9 as overweight, and 30.0 or above as obese. BMI does not measure body composition or metabolic health directly, and its limitations are well documented at the individual level.[69]
Both extremes of BMI impair fertility. At the low end, insufficient energy availability drives hypothalamic amenorrhea and anovulation. At the high end, insulin resistance and hyperinsulinemia drive anovulatory cycles and androgen excess, the core metabolic disruption in many cases of PCOS. Subfertility risk rises with deviation from the normal range in both directions.[69]
Obesity is also associated with elevated miscarriage risk and lower cycle-based pregnancy rates. The mechanism is metabolic. Adipose tissue acts as an endocrine organ, generating estrogen excess, disrupting the hypothalamic-pituitary-ovarian axis, and amplifying insulin resistance. Addressing underlying metabolic dysfunction through lifestyle modification treats the root cause rather than bypassing it.[70]
BMI appears alongside hormonal abnormalities in the evaluation of couples with unexplained infertility. It contextualizes findings from cycle charting and informs decisions about nutritional and lifestyle intervention. The goal is restoring the conditions for normal ovulation, not simply achieving a target weight.
This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.