Is Homocystein useful for fertility?

Homocysteine is a biomarker sometimes linked to fertility. Elevated levels have been associated with recurrent pregnancy loss, poor oocyte quality, and impaired sperm parameters. However, the evidence is moderate: associations exist but causality is not firmly established. Homocysteine can be elevated due to MTHFR gene variants or deficiencies in folate, B12, or B6. Testing homocysteine may be useful as part of a broader fertility workup, but it is not a standalone diagnostic tool. Direct-to-consumer tests often lack clinical validation for fertility claims. Do not start high-dose B vitamin supplements without proper testing and medical guidance, as excess folate can mask B12 deficiency. Evidence: human-moderate.