Myths vs facts: MTHFR and fertility

Myths vs facts: MTHFR and fertility. The myth: MTHFR variants (especially C677T) directly cause infertility or recurrent miscarriage, and switching to methylfolate instead of folic acid can fix fertility issues. The facts: MTHFR is an enzyme involved in folate metabolism. The C677T variant (rs1801133) has an allele frequency of about 0.3 in Europeans and moderately reduces enzyme activity. Some studies suggest a weak link between MTHFR polymorphisms, elevated homocysteine, and fertility problems, but the evidence is inconsistent and effect sizes are small. Current clinical guidelines do not recommend routine MTHFR testing for fertility. Adequate folate intake (400–800 µg folic acid/day) is standard for all women planning pregnancy, regardless of genotype. Claims that methylfolate is superior to folic acid are not supported by large randomized trials. Be cautious of expensive genetic tests marketing MTHFR as a 'key gene' for fertility. The evidence is weak to moderate, and clinical relevance remains debated.