How are FT4 and fertility related?

FT4 (free thyroxine) is a key thyroid hormone and plays a significant role in fertility. Both hypothyroidism (low FT4) and hyperthyroidism (high FT4) can disrupt menstrual cycles, ovulation, and implantation. Thyroid function is routinely assessed in women with infertility. Subclinical hypothyroidism (elevated TSH, normal FT4) is also linked to fertility issues, though evidence for universal treatment remains debated. Importantly, FT4 alone without TSH is insufficient for diagnosis; clinical evaluation is essential. MyBody-X offers thyroid markers in blood tests but does not replace medical diagnosis. The evidence for the FT4–fertility link is human-strong, supported by clinical guidelines (e.g., ATA, ETA). Caveat: Genetic variants (e.g., in the TSH receptor) can influence individual FT4 levels but are rarely the sole cause of infertility.