Evidence check: FT3 in the context of fertility

The question about FT3 (free triiodothyronine) in the context of fertility is relevant, but the evidence base is limited. Thyroid hormones influence reproductive function, and hypothyroidism can impair fertility. In clinical routine, TSH (thyroid-stimulating hormone) is the primary screening parameter, often supplemented by fT4. FT3 alone is not an established marker for fertility disorders. Some studies suggest an association between low FT3 levels and female infertility, particularly in ovarian dysfunction, but the data are heterogeneous and insufficient for a clear clinical recommendation. Direct-to-consumer tests that offer isolated FT3 often overestimate its predictive value. Caveat: A single FT3 value without TSH and fT4 is diagnostically weak. The evidence is rated as 'unclear' or 'mixed' because there are no strong, reproducible studies from large cohorts that establish FT3 as an independent fertility marker. For those planning pregnancy, a full thyroid workup (TSH, fT4, possibly antibodies) should be performed by a physician.