What Is Folic Acid and Why Is It Recommended in Pregnancy?

Folic acid is the synthetic form of folate (vitamin B9).

Folate is essential for:

• DNA synthesis
• Rapid cell division
• Tissue growth
• Neural tube development

During very early pregnancy, the neural tube forms the baby’s brain and spinal cord.

Here’s the key biological fact:

The neural tube closes by day 28 after conception.

That’s often before a woman even knows she’s pregnant.

If folate status is inadequate during that narrow window, the risk of neural tube defects (NTDs), including spina bifida and anencephaly, increases significantly.

Large randomised controlled trials show that folic acid supplementation reduces neural tube defects by up to 70% (MRC Vitamin Study Research Group, 1991).

This is why official guidance recommends:

• 400 micrograms of folic acid daily
• Starting 2–3 months before conception
• Continuing through the first 12 weeks of pregnancy

This recommendation is consistent across the UK, Europe, the US, and WHO guidance.

Can You Get Enough Folate from Food Alone?

Leafy greens, legumes, citrus fruits and wholegrains contain natural folate.

But dietary intake alone often does not raise red blood cell folate to the levels shown to protect against neural tube defects.

This is why supplementation is advised even for women with balanced diets.

This isn’t about replacing food.

It’s about covering a critical developmental window with strong preventative evidence.

Does Folic Acid Cause Harm to the Baby?

Let’s address the most common concerns.

1. “Folic acid is synthetic and builds up in the blood”

Unmetabolised folic acid can be detected at high supplemental intakes, usually above 1 mg per day long-term.

The recommended dose for pregnancy prevention is 400 micrograms.

There is no high-quality human evidence showing that 400 micrograms daily causes congenital abnormalities or fetal harm.

2. “Folic acid masks vitamin B12 deficiency”

High doses of folic acid can mask haematological signs of B12 deficiency.

However:

• This is primarily a concern in older adults.
• It does not negate the protective effect against neural tube defects.
• It has not been shown to cause fetal harm at recommended pregnancy doses.

3. “If you have MTHFR, you shouldn’t take folic acid”

MTHFR polymorphisms are common in the population.

Most individuals — including those with common variants — can metabolise folic acid adequately at recommended doses.

Major health organisations do not recommend routine replacement of folic acid with methylfolate for the general population.

If a woman has a previous neural tube defect pregnancy or a known metabolic disorder, this is managed medically with adjusted dosing.

That is a clinical scenario — not general advice.

What Does Population Data Show?

Countries that introduced folic acid fortification saw:

• Significant reductions in neural tube defects
• No increase in overall birth defect rates
• No credible signal of widespread harm

If folic acid supplementation at recommended levels were harmful, we would expect to see a rise in congenital abnormalities at a population level.

We don’t.

Risk vs Risk

Without supplementation:

• Increased risk of neural tube defects

With 400 micrograms of folic acid:

• Up to 70% reduction in neural tube defect risk
• No proven causal link to fetal harm at recommended dose

From a risk-benefit perspective, the evidence is clear.

My Evidence-Based Recommendation

If you are:

• Trying to conceive
• Not actively preventing pregnancy
• Or in your first trimester

Take 400 micrograms of folic acid daily.

Start before conception if possible.

Continue until 12 weeks pregnant.

Pair it with a varied, balanced diet.

If you are unsure or have medical history concerns, speak to your GP or midwife.

Pregnancy nutrition should feel grounded and empowering — not confusing.

References (PubMed Indexed)

1. MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet. 1991;338(8760):131–137. PMID: 1677062.
2. Czeizel AE, Dudás I. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. N Engl J Med. 1992;327(26):1832–1835. PMID: 1307234.
3. De-Regil LM, Peña-Rosas JP, Fernández-Gaxiola AC, Rayco-Solon P. Effects and safety of periconceptional folate supplementation for preventing birth defects. Cochrane Database Syst Rev. 2015;(12):CD007950. PMID: 26662928.
4. Crider KS, Bailey LB, Berry RJ. Folic acid food fortification—its history, effect, concerns, and future directions. Nutrients. 2011;3(3):370–384. PMID: 22254138.
5. Bailey SW, Ayling JE. The extremely slow and variable activity of dihydrofolate reductase in human liver. Proc Natl Acad Sci USA. 2009;106(36):15424–15429. PMID: 19706381.
6. Obeid R, Pietrzik K. Neural tube defects and folate metabolism. J Perinat Med. 2010;38(2):141–150. PMID: 19968650.