What role does SHBG play in fertility?

SHBG (sex hormone-binding globulin) modulates the bioavailability of sex steroids like testosterone and estradiol. Low SHBG increases free testosterone, which in women is linked to PCOS and ovulatory dysfunction. In men, low SHBG often accompanies insulin resistance and metabolic syndrome, factors that can impair spermatogenesis. However, SHBG is not a direct fertility marker; evidence is largely epidemiological and mechanistic. Clinically, SHBG is measured as part of a hormone panel, but interpretation requires LH, FSH, estradiol, and free androgen index. Direct-to-consumer tests (e.g., MyBody-X) can measure SHBG, but without clinical context the value is limited. The evidence for a causal role of SHBG in fertility is moderate – it is a surrogate, not a standalone predictor. Caveat: levels fluctuate with liver function, thyroid status, and diet.