My midwife at the booking appointment was wonderfully direct about most things, but on one topic she was almost fierce. "Are you taking folic acid?" she asked, pen hovering over the form. I nodded — I'd started a few weeks before, when the pregnancy test came back positive. She paused, looked at me over her glasses, and said: "Good. That one's not optional." Then she circled something on her checklist and moved on, leaving me with the distinct impression that of all the vitamins, supplements, and lifestyle changes swirling around early pregnancy, this was the one she would physically wrestle me into taking if necessary.
She wasn't being dramatic. Folic acid — the synthetic form of vitamin B9 — is the single most evidence-backed supplement in prenatal care. Its role in preventing neural tube defects (NTDs) like spina bifida and anencephaly is supported by decades of research and endorsed by every major health organisation worldwide. It's one of the few areas in nutrition where the science is essentially settled, the recommendation is universal, and the consequence of not taking it is concrete and measurable.
And yet — and this genuinely surprised me — many women don't start taking it early enough, or don't take it at all. Some don't know about it until their first midwife appointment, by which point the most critical window may have partially closed. Others confuse it with general prenatal vitamins and assume they're covered. So this is the article where we get properly into the detail: what vitamin B9 actually does, why the timing matters so much, how much you need, and where to find it in your food.
What vitamin B9 actually is (and why the names matter)
Vitamin B9 exists in two forms, and the distinction isn't just academic — it affects how your body processes it.
Folate is the naturally occurring form found in food. It's present in leafy greens, legumes, citrus fruits, and various other whole foods. Your body absorbs it through the gut, where it undergoes several conversion steps before becoming the active form (5-MTHF) that your cells can actually use.
Folic acid is the synthetic, manufactured form used in supplements and fortified foods. It's more stable than natural folate (which degrades with heat and light), which is why it's used in supplements. It's also slightly more bioavailable — your body absorbs it more efficiently than food folate, which is partly why supplements are recommended even for women with excellent diets.
There's a third form you may encounter: methylfolate (5-MTHF or L-methylfolate), which is the already-active form. Some supplements use this instead of folic acid, and it's marketed toward women with MTHFR gene variants who may process folic acid less efficiently. We'll come back to this, because the internet has turned MTHFR into something of a panic topic and the reality is more nuanced.
For clarity throughout this article: "folate" means the natural food form, "folic acid" means the supplement form, and "vitamin B9" is the umbrella term for both.
Why it's critical during pregnancy
Vitamin B9 is essential for cell division and DNA synthesis — it's one of the building blocks your body needs to create new cells. During pregnancy, when you're building an entire new human being from scratch, the demand for cell division is extraordinary. In the first twelve weeks alone, a single fertilised cell divides into trillions of specialised cells forming organs, limbs, the nervous system, and the brain. Folate is required at every stage of this process.
Specifically, vitamin B9 is involved in:
- Neural tube formation: The neural tube — which becomes the brain and spinal cord — forms and closes between days 21 and 28 after conception. This is often before a woman even knows she's pregnant. Adequate folate levels during this window are directly linked to proper neural tube closure.
- DNA replication: Every time a cell divides, its DNA must be accurately copied. Folate is a co-factor in this process. Insufficient folate increases the risk of errors in DNA replication.
- Red blood cell production: Pregnancy increases blood volume by roughly 50%. Your body needs to produce significantly more red blood cells, and folate is essential for this. Folate deficiency during pregnancy can cause megaloblastic anaemia — a condition where red blood cells are abnormally large and don't function properly.
- Placental development: The placenta — your baby's life support system — is one of the most rapidly growing tissues in the human body. Its development requires intense cell division, and therefore adequate folate.
- Amino acid metabolism: Folate helps regulate homocysteine levels in the blood. Elevated homocysteine during pregnancy is associated with preeclampsia, placental abruption, and recurrent miscarriage. Adequate folate keeps homocysteine in check.
The reason folic acid supplementation is pushed so hard — harder than any other prenatal nutrient — is that the consequences of deficiency are severe and the critical window is extremely narrow. For most other nutrients, your body has reserves and the effects of insufficiency are gradual. For folate and neural tube development, there's a roughly three-week window where levels matter enormously, and by the time most women have their first prenatal appointment, that window has often closed.
Neural tube defects: the risk folic acid prevents
Neural tube defects are among the most serious birth defects, and they're the primary reason folic acid supplementation is recommended. The neural tube is the embryonic structure that develops into the brain and spinal cord. It forms during the first month of pregnancy and normally closes completely by around day 28 post-conception.
When the neural tube doesn't close properly, the result is a neural tube defect. The two most common are:
Spina bifida: The spinal column doesn't close completely, leaving the spinal cord partially exposed. The severity ranges widely — from spina bifida occulta (a small gap with no symptoms, sometimes discovered incidentally in adulthood) to myelomeningocele (the most severe form, where the spinal cord and its covering protrude through the opening, causing paralysis below the defect, bladder and bowel dysfunction, and often requiring surgery within the first days of life).
Anencephaly: The brain doesn't develop properly. This is the most severe neural tube defect and is fatal — babies born with anencephaly typically survive only hours or days after birth. It accounts for roughly a third of neural tube defects in the UK.
The evidence that folic acid prevents these defects is exceptionally strong. The landmark Medical Research Council trial, published in 1991 in the BMJ, demonstrated a 72% reduction in neural tube defect recurrence among women taking folic acid supplements. Subsequent population studies — particularly in countries that introduced mandatory folic acid fortification of flour — have shown consistent reductions of 20–50% in NTD rates.
In the UK, approximately 1,000 pregnancies per year are affected by neural tube defects. The government introduced mandatory folic acid fortification of non-wholemeal wheat flour in 2024, following decades of debate and evidence from countries like the US, Canada, and Australia that had already implemented it with measurable reductions in NTD rates.
When to start taking it — timing is everything
The NHS recommends starting folic acid supplementation as soon as you begin trying to conceive — ideally at least three months before conception. NICE guidelines are even more specific: they recommend folic acid from the point of planning pregnancy through to the end of the 12th week of pregnancy (the first trimester).
Why three months before? Because it takes time for folic acid supplementation to build up adequate levels in your body. While folic acid is absorbed relatively quickly, establishing consistently optimal levels in your red blood cells and tissues takes several weeks of regular supplementation. Starting early ensures that your folate levels are already adequate during those crucial first weeks after conception, when the neural tube is forming.
The reality, of course, is that roughly half of pregnancies in the UK are unplanned. If your pregnancy was a surprise and you weren't taking folic acid beforehand, don't spiral into guilt — start taking it as soon as you find out and continue through the first trimester. Many women with unplanned pregnancies have adequate folate levels from their diet alone, particularly if they eat a varied diet rich in vegetables and legumes. The supplement provides additional insurance, not the entire supply.
The supplementation timeline:
- Pre-conception (ideally 3+ months before): Start taking 400 µg daily.
- First trimester (weeks 1–12): Continue taking 400 µg daily. This covers the neural tube closure period and the most intensive phase of organ formation.
- After week 12: The NHS says you can stop folic acid supplementation after the first trimester if you choose, as the neural tube has fully closed. However, many prenatal multivitamins include folic acid throughout pregnancy, and continuing it does no harm. Folate remains important for red blood cell production and cell division throughout pregnancy.
How much do you need?
The standard recommendation is 400 micrograms (µg) per day for most women. This is the dose shown in research to reduce neural tube defect risk, and it's the dose recommended by the NHS, NICE, RCOG, and WHO. It's also the dose found in most over-the-counter folic acid supplements and prenatal vitamins.
However, some women need a higher dose. The NHS recommends 5 milligrams (mg) per day — that's 5,000 µg, or more than twelve times the standard dose — if any of the following apply:
- You or your partner have a neural tube defect, or you've had a previous pregnancy affected by an NTD
- You have diabetes (type 1 or type 2)
- You take anti-epileptic medication (some anticonvulsants interfere with folate metabolism)
- You have coeliac disease or another condition affecting nutrient absorption
- You have sickle cell disease or thalassaemia
- Your BMI is above 30
The 5 mg dose requires a prescription — it's not available over the counter. If any of these risk factors apply to you, speak to your GP before or as soon as possible after becoming pregnant. The higher dose is particularly important during the pre-conception and first-trimester period.
Can you take too much folic acid? At the standard 400 µg dose, no. The tolerable upper intake level set by the European Food Safety Authority is 1,000 µg (1 mg) per day for adults from supplements and fortified food. At the prescribed 5 mg dose for high-risk women, there are no established harmful effects in the context of pregnancy — the benefits far outweigh any theoretical concerns. Some older research raised questions about very high folic acid intake masking vitamin B12 deficiency, but at recommended doses this is not clinically significant.
The best food sources of natural folate
Supplements are recommended because they provide a reliable, consistent dose. But food sources of folate are also valuable — they contribute to your overall intake, provide additional nutrients, and help establish eating patterns that benefit both you and your baby beyond just the B9 content.
The richest food sources of folate:
- Dark leafy greens: Spinach (194 µg per 100g cooked), kale, spring greens, Swiss chard. Spinach is particularly dense in folate — a single generous portion provides nearly half the daily requirement.
- Legumes: Lentils (181 µg per 100g cooked), chickpeas (172 µg), black beans (149 µg), kidney beans. Legumes are folate powerhouses and also provide protein, fibre, and iron.
- Asparagus: 149 µg per 100g cooked. One of the highest-folate vegetables per serving.
- Broccoli: 108 µg per 100g cooked. Also rich in vitamin C, which aids iron absorption — a useful bonus during pregnancy.
- Brussels sprouts: 78 µg per 100g cooked. Underrated and genuinely delicious when roasted rather than boiled into submission.
- Beetroot: 80 µg per 100g cooked. Also provides nitrates that support blood flow.
- Avocado: 81 µg per 100g (about half an avocado). Also provides healthy fats and potassium.
- Oranges and citrus fruit: 54 µg per large orange. One of the few fruits with meaningful folate content.
- Eggs: 47 µg per egg (whole, cooked). The folate is concentrated in the yolk.
- Fortified breakfast cereals: Variable — check the label. Many UK cereals are fortified with folic acid at 100–200 µg per serving.
A practical note: natural folate is sensitive to heat, light, and water. Steaming or stir-frying vegetables retains more folate than boiling. Storing vegetables in the fridge rather than at room temperature preserves folate levels. Eating some folate-rich foods raw — spinach in salads, avocado, oranges — ensures no cooking losses. These factors are why supplements are recommended even for women with excellent diets: you can't reliably guarantee that enough food folate survives cooking and digestion to meet the pregnancy requirement.
Choosing the right supplement
Walking into the supplement aisle as a pregnant woman is an overwhelming experience. The options range from basic folic acid tablets costing less than £2 to elaborate prenatal multivitamin packages costing £30+ per month. Here's what actually matters.
Basic folic acid (400 µg): Available from any pharmacy, supermarket, or online retailer. Costs very little. NHS-endorsed. Does exactly what's needed. If budget is a concern, this is all you need — the expensive options don't provide better folic acid. In fact, the NHS Healthy Start scheme provides free vitamins including folic acid to qualifying pregnant women.
Prenatal multivitamins: These typically combine folic acid with other pregnancy-relevant nutrients — vitamin D (10 µg, also recommended by the NHS), iron, iodine, calcium, and various other vitamins. They're convenient (one tablet instead of several) and they're fine, but they're not strictly necessary if you're already taking folic acid and vitamin D separately and eating a balanced diet. They are, however, a good safety net if your diet is variable or restricted.
Methylfolate (5-MTHF) supplements: These contain the already-active form of folate. They're marketed primarily to women with MTHFR gene variants — polymorphisms that can reduce the efficiency with which the body converts folic acid to its active form. The MTHFR topic has become disproportionately alarming online. The reality: the most common MTHFR variant (C677T) is present in roughly 10% of the UK population, and even in homozygous carriers, folic acid still works — it's just slightly less efficiently converted. For most women, standard folic acid is perfectly adequate. If you know you have an MTHFR variant and it concerns you, methylfolate supplements are a reasonable alternative, but they're not necessary for the general population.
What to avoid: Supplements containing vitamin A (retinol) at doses above 700 µg. High-dose vitamin A is teratogenic — it can cause birth defects. This is why pregnant women are advised to avoid liver and liver products (very high in retinol) and to check that their supplements use beta-carotene rather than retinol. Most pregnancy-specific supplements are formulated correctly, but always check the label if you're taking a general multivitamin not specifically designed for pregnancy.
Beyond B9: the full prenatal vitamin picture
While folic acid gets — and deserves — the most attention, it's worth knowing which other nutrients matter during pregnancy and which the NHS specifically recommends supplementing.
Vitamin D (10 µg / 400 IU daily): The NHS recommends this for everyone in the UK, not just pregnant women, but it's particularly important during pregnancy for foetal bone development and immune function. Most people in the UK are deficient during autumn and winter due to limited sunlight. Take it throughout pregnancy and while breastfeeding.
Iron: Not routinely supplemented in the UK unless you're diagnosed with iron deficiency anaemia (checked via blood test at your booking appointment and again around 28 weeks). If your iron levels are low, your midwife will prescribe a supplement. If they're normal, you don't need one — excess iron during pregnancy can cause constipation, nausea, and isn't beneficial.
Iodine: Important for thyroid function and baby's brain development. The UK diet often provides insufficient iodine, particularly if you don't consume dairy or fish regularly. Some prenatal vitamins include iodine; if yours doesn't, consider whether your diet provides enough (dairy, fish, and eggs are the main sources).
Calcium: Your baby needs calcium for bone development, and if your dietary intake is insufficient, your body will draw from your own bone stores. If you consume dairy regularly (milk, cheese, yoghurt), you're likely getting enough. If you're dairy-free, supplementation or calcium-fortified alternatives are worth considering.
Omega-3 DHA: Not officially supplemented by NHS recommendation, but well-supported by evidence for foetal brain and eye development. If you eat two portions of fish per week (including one oily fish), you're probably getting enough. If not, a DHA supplement is a good idea — as discussed in our seafood during pregnancy guide.
Frequently asked questions
Is it too late to start folic acid if I'm already 8 weeks pregnant?
Start taking it now regardless. While the most critical period for neural tube closure is weeks 3–4 after conception, folic acid continues to support cell division, red blood cell production, and placental development throughout the first trimester. Starting at 8 weeks still provides meaningful benefit. Don't let the fact that you didn't start earlier prevent you from starting now.
Can I get enough folic acid from food alone?
It's very difficult to consistently meet the pregnancy requirement (400 µg+ daily) from food alone, because natural folate is partially destroyed by cooking and is less bioavailable than supplemental folic acid. A diet extremely rich in leafy greens and legumes might come close, but supplements provide a reliable baseline that doesn't depend on perfect eating habits every single day — which, during early pregnancy nausea, is an unrealistic expectation.
What happens if I forget to take folic acid for a few days?
Missing a few days is unlikely to have any significant impact. Your body stores some folate in the liver and red blood cells, so a brief gap doesn't deplete your levels. Simply resume taking it at your normal dose — don't double up. If you've missed weeks rather than days, speak to your midwife, but even then, the most likely outcome is that everything is fine, particularly if your diet includes folate-rich foods.
Should I take folic acid if I'm on the contraceptive pill?
If you're actively trying not to become pregnant and are reliably using contraception, routine folic acid supplementation isn't necessary. However, if there's any possibility of pregnancy — if you're thinking about stopping contraception in the coming months, or if your contraceptive use is inconsistent — starting folic acid is a sensible precaution. The three-month build-up recommendation means that by the time you do conceive, your levels will already be optimal.
Do I need the 5 mg prescription dose or the 400 µg standard dose?
Most women need the standard 400 µg dose. The 5 mg prescribed dose is for women with specific risk factors: previous NTD-affected pregnancy, diabetes, BMI over 30, anti-epileptic medication, or coeliac disease. If you're unsure whether you qualify for the higher dose, ask your GP — they can prescribe it quickly, and it's available free on NHS prescription during pregnancy.
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