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Truly speaking, MTHFR - methylene tetrahydrofolate reductase mutations are widely spread and all most one half of the population is having or carrying these mutations by different extent. By different extent, I mean to say, various levels of affection or involvement that is from very insignificant disease to severe disease.
I do want to know that in which category you are now. This is fairly judged by the serum levels of homocysteine, which is the protein that is increased in the blood. If you have a severe MTHFR defect, then you need to avoid Folic acid and also need to screen some fetal congenital defects like spina bifida or anencephaly at an earliest.
But, if you do not have any specific symptoms with this mutation, then there is no harm to take these vitamins. PAI mutations (plasminogen activator inhibitor) could result in abnormalities in blood clotting disorders. This actually poses no bar for taking Folic acid in pregnancy state.
For further information consult an obstetrician and gynaecologist online --> https://www.icliniq.com/ask-a-doctor-online/obstetrician-and-gynaecologist