Evidence check: FT3 in the context of Fruchtbarkeit

FT3 (free triiodothyronine) is a thyroid hormone that plays a minor role in fertility diagnostics. The evidence for a direct link between isolated FT3 levels and fertility is moderate. Thyroid dysfunction (hypo- or hyperthyroidism) is known to impair fertility, but the standard parameter is TSH, supplemented by FT4. FT3 may be elevated in hyperthyroidism or low in hypothyroidism, but isolated FT3 abnormalities without TSH/FT4 changes are rare and often clinically insignificant. Consumer lab tests measuring only FT3 do not provide a complete picture. Comprehensive thyroid assessment (TSH, FT4, possibly antibodies) is necessary. The evidence for FT3 as a standalone fertility marker is weak; clinical practice relies on TSH. Caveat: No randomized trials support the use of FT3 measurement for fertility optimization. If trying to conceive, thyroid function should be evaluated by a physician.