MTHFR and Pregnancy: Folic Acid, Methylfolate and What the Evidence Says

If you've found out you carry an MTHFR gene variant and you're pregnant or planning to be, you've probably come across confident advice online telling you to stop folic acid and take methylfolate instead. The reality is more nuanced, and it matters to get it right, because folate in early pregnancy is one of the best-established nutrition recommendations there is.

This guide sets out what the official advice is, where MTHFR fits in, what we know and don't know about methylfolate, and the questions worth bringing to your GP or midwife.

Start with the official advice

The HSE recommends that anyone who could become pregnant takes a 400 microgram folic acid supplement every day, starting at least three months before pregnancy and continuing during pregnancy. Some people are advised to take a higher 5 mg prescription dose, including those with a personal or family history of a neural tube defect, diabetes or obesity.

The reason is timing. The neural tube, which becomes the baby's brain and spinal cord, closes within about the first four weeks of pregnancy, often before a pregnancy is confirmed. Large trials have shown that folic acid taken before conception and in early pregnancy reduces the risk of neural tube defects such as spina bifida. That evidence is strong, and it was gathered using folic acid.

What MTHFR has to do with it

Folic acid is a synthetic form of folate. The body converts it in several steps into the active form, 5-methyltetrahydrofolate (methylfolate). The final step uses an enzyme called MTHFR.

Common variants in the MTHFR gene, especially C677T, produce an enzyme that works less efficiently, particularly in people who carry two copies (homozygous). These variants are common: a substantial minority of people in Ireland and across Europe carry at least one copy. People with two copies of C677T tend to have lower folate levels and higher homocysteine, especially when folate intake is low.

Important context: carrying an MTHFR variant does not mean you can't use folic acid. People with these variants still absorb and convert folic acid, and adequate folate intake raises their folate levels. Studies have also shown that people with the variant benefit from folic acid. The difference is one of efficiency, not an all-or-nothing block.

What about unmetabolised folic acid?

When intake of folic acid is high, some of it can circulate in the blood unchanged, known as unmetabolised folic acid. Researchers have asked whether this has any effects, for example on immune cells. At the moment this is an open research question rather than an established risk, and it isn't a reason to stop taking the folic acid your GP or midwife has recommended.

Where methylfolate comes in

Methylfolate is the form of folate already active in the body, so it doesn't need the MTHFR step. It is used in some prenatal supplements, and some clinicians suggest it for people with MTHFR variants, people who don't tolerate folic acid, or people taking medicines that interact with folate.

What we know:

• Methylfolate raises blood folate levels at least as well as folic acid in studies.
• It doesn't depend on MTHFR enzyme activity.
• It doesn't produce unmetabolised folic acid.

What we don't yet know:

• The large trials proving protection against neural tube defects used folic acid. Equivalent outcome trials for methylfolate haven't been done, so its protective effect is inferred from blood levels rather than proven directly.

So the choice between folic acid and methylfolate, and the dose, is a decision to make with your GP, obstetrician or midwife, not one to make from a blog post, including this one.

The rest of the picture: B12, B6 and homocysteine

Folate works closely with vitamin B12. Together they recycle homocysteine, and low B12 can affect how folate is used. Vitamin B6 clears homocysteine through a separate route. Maternal folate intake contributes to the normal growth of maternal tissue during pregnancy, and folate contributes to normal blood formation and normal homocysteine metabolism.

If you have an MTHFR variant, it is reasonable to ask your GP whether checking your B12, folate and, where relevant, homocysteine before or early in pregnancy makes sense for you.

Practical steps

• Don't stop your folic acid on your own. If you'd like to consider methylfolate instead, raise it with your GP or midwife first.
• Start early. Whatever form you use, begin at least three months before trying to conceive where possible.
• Ask whether you need a higher dose. Personal or family history of neural tube defects, diabetes and obesity are reasons the HSE gives for the 5 mg dose.
• Use a supplement made for pregnancy. Prenatal supplements are formulated with pregnancy in mind, including appropriate vitamin A limits and iodine.
• Bring your MTHFR result to appointments. It is useful context, even though it rarely changes the core recommendation.

Questions to bring to your GP or midwife

• Given my MTHFR result, is folic acid or methylfolate better for me, and at what dose?
• Should I have my B12, folate or homocysteine checked?
• Do I need the higher 5 mg dose?
• Do any of my current medicines affect folate?

Key takeaways

• The HSE recommends 400 micrograms of folic acid daily from at least three months before pregnancy; some people need 5 mg on prescription.
• MTHFR variants make folate conversion less efficient, but people with them still benefit from folic acid.
• Methylfolate is an active form that bypasses MTHFR. It raises folate levels well, but the neural tube defect trials used folic acid.
• B12 and B6 work alongside folate in homocysteine metabolism.
• Choose your form and dose with your GP or midwife.

Read next: What is MTHFR? and active vs inactive B vitamins.

This article is for general information and is not medical advice. NeuroThrive™ supplements are not prenatal supplements and are not formulated for pregnancy. Always follow the advice of your GP, obstetrician or midwife on supplements during pregnancy.