Folic Acid and Prenatal Vitamins Before Conception

The honest picture, with numbers

Folic acid is the one preconception supplement with trial evidence strong enough to be recommended everywhere, and it is worth knowing exactly what it does and does not do. It does not improve your chance of conceiving. It reduces the chance that a pregnancy is affected by a neural tube defect — a problem with the developing brain or spine, such as spina bifida.

Cochrane's review of periconceptional oral folate supplementation pooled five trials covering 6,708 births and found a risk ratio for neural tube defects of 0.31 (95% CI 0.17 to 0.58). Split by pregnancy history, the risk ratio was 0.34 (95% CI 0.18 to 0.64) for recurrence across four trials and 1,846 births, and 0.07 (95% CI 0.00 to 1.32) for first occurrence in the single trial of 4,862 births — no cases at all in the supplemented group.

The same review is honest about the limits. For other birth defects the evidence was low quality and showed no clear effect: cleft palate risk ratio 0.73 (95% CI 0.05 to 10.89), cleft lip 0.79 (95% CI 0.14 to 4.36), cardiovascular defects 0.57 (95% CI 0.24 to 1.33), other anomalies 0.94 (95% CI 0.53 to 1.66). Miscarriage risk was unchanged at 1.10 (95% CI 0.94 to 1.28), moderate-quality evidence. Folic acid is not a general-purpose protective supplement, and it is not a fertility drug.

What actually matters: dose and timing

The standard dose

The NHS recommends 400 micrograms of folic acid every day, ideally starting three months before you conceive and continuing through the first 12 weeks of pregnancy. Taking it for longer than that does no harm. Cochrane's analysis found the protective effect held at daily doses of 400 micrograms (0.4 mg) or higher, so a higher dose is not automatically better — it is targeted at specific groups.

Who needs 5 mg

The NHS lists the situations in which a GP should prescribe the higher 5 mg daily dose if you are planning a pregnancy or less than 12 weeks pregnant:

• you or the baby's father has a neural tube defect
• you or the baby's father has a relative with a neural tube defect
• you have had a previous pregnancy affected by a neural tube defect
• you have diabetes
• you have a blood condition such as sickle cell anaemia or thalassaemia
• you take medicine for epilepsy or HIV

ACOG frames the same point slightly differently: at least 400 micrograms daily from at least one month before pregnancy, and 4 mg as a separate supplement — not by taking multiple prenatal vitamins — for people who have previously had a child with a neural tube defect, started at least three months before conception.

Why timing matters more than duration

The neural tube closes in the first weeks after conception, frequently before a pregnancy test is positive. That is the whole argument for starting before you conceive rather than when you find out. If you have been trying for months, you should already be taking it; if you have recently started and are not, start today rather than waiting for a next cycle.

Vitamin D

The NHS recommends 10 micrograms (400 IU) of vitamin D daily from early October to late March, and all year round if you usually cover most of your skin outdoors, spend a lot of time indoors, or have black or brown skin — because skin pigmentation affects how much vitamin D your skin makes. The upper limit is 100 micrograms a day.

Iron

ACOG notes that people who are not pregnant need 18 mg of iron a day and pregnant people need 27 mg, an amount found in most prenatal vitamins. Iron is not a preconception fertility intervention; it is preparation for the demands of pregnancy, and levels are checked at your booking appointment and again at around 28 weeks.

What to avoid, and what not to bother with

The clearest instruction is a negative one. The NHS says do not take cod liver oil or any supplement containing vitamin A (sometimes labelled retinol) when pregnant, because too much vitamin A can harm your baby's development. Read the label on any multivitamin you already take. A general adult multivitamin is not a prenatal vitamin.

Beyond folic acid, vitamin D and — where indicated — iron, the evidence thins quickly. NICE states that the effectiveness of complementary therapies for fertility problems has not been properly evaluated. For male-factor problems specifically, NG257 recommends against supplements or antioxidants aimed at improving sperm DNA integrity, and against sperm DNA fragmentation testing altogether. If a product is being sold to you on the basis that it improves egg quality, ask what trial showed that and what the outcome measured was.

Prenatal vitamin brands compete on ingredient count. Ingredient count is not evidence. A cheap supplement containing 400 micrograms of folic acid and 10 micrograms of vitamin D does the thing the evidence supports.

What to do next

1. Start 400 micrograms of folic acid daily now, whatever stage you are at — pharmacies sell it cheaply and no prescription is needed.
2. Check the 5 mg list. If any item applies to you, book a GP appointment specifically to ask for the prescribed dose; it is not available over the counter at that strength.
3. Add 10 micrograms of vitamin D and check whether you need it year-round.
4. Read the label of everything else you take for vitamin A or retinol, and stop cod liver oil.
5. Ask about Healthy Start if you are in the UK — free vitamin supplements containing folic acid, vitamin C and vitamin D are available to those who qualify.
6. Do not treat supplements as your fertility plan. They protect a pregnancy; they do not create one.

When to seek help

Speak to a GP rather than self-managing if you have epilepsy, diabetes, coeliac disease, a blood disorder, a previous pregnancy affected by a neural tube defect, or a BMI over 30 — several of these change the recommended dose, and some change other parts of your pre-pregnancy care. NG257 also recommends coeliac disease testing as part of fertility investigation, which matters here because untreated coeliac disease affects absorption.

Separately, taking folic acid correctly does not change the referral clock. NG257 recommends assessment of both partners after 1 year of unprotected vaginal intercourse, and referral at first presentation from age 36 or where there is a known or suspected cause. If you have been taking supplements diligently for a year without conceiving, that is a year of trying, and it counts.