How much folic acid should I take before getting pregnant?

The standard dose: 400 mcg a day

The CDC recommends that every woman who could become pregnant get 400 mcg of folic acid every day. Folic acid is the man-made form of folate, a B vitamin, used in supplements and fortified bread, flour and cereal. The CDC says it is the only type of folate shown to help prevent neural tube defects, such as spina bifida.

You'll see the same amount written as 0.4 mg. Most prenatal vitamins contain at least this much. The UK's NHS uses the same 400 mcg, from before pregnancy until 12 weeks.

So for most people the answer is simple: one prenatal or folic acid tablet with 400 mcg, every day.

When to start, and why it can't wait for the first appointment

By about day 28 after conception, the neural tube, which becomes the brain and spinal cord, has folded up and sealed shut. That's roughly six weeks after the first day of your last period, often before a positive test. The CDC says to start folic acid at least one month before you conceive, and warns that waiting until your first prenatal visit will not prevent neural tube defects. That appointment usually comes too late for the tube.

One month is the floor. Three months gets you closer to full shelves. In a German trial at the University of Bonn, 144 women took folic acid or methylfolate daily for 24 weeks. Their red blood cell folate, the long-term store, was still rising at the end. The researchers suggested that more than 12 weeks of supplements before conception may give the fullest protection.

There may be more to it than the spine. In Norway's observational MoBa study of 85,176 children, folic acid taken from four weeks before to eight weeks after conception was linked with fewer cases of autistic disorder (0.10% versus 0.21%), a link the authors say cannot prove cause. The message is the same as for the spine: the weeks around conception are the window that counts.

If you're reading this already pregnant and haven't been taking folic acid, don't panic. Start a 400 mcg supplement today and tell your doctor or midwife at your first contact. They can tell you whether anything else needs to change, and good nutrition from here on still counts for the rest of your baby's brain building.

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Who needs a higher dose

Weight-loss surgery is another reason to ask your doctor about your dose. If you take a seizure medicine, don't change it on your own. Talk to your specialist, ideally months before trying, because some medicines need a plan and any switch takes time.

In a US and UK study of children exposed to seizure medicines in the womb, folic acid around conception was linked with a higher average IQ at age 6 (108 versus 101) after accounting for which medicine was taken, an association rather than proof. The NHS advises a higher prescribed dose for women on anti-seizure medicine.

Why more isn't better on your own

It's tempting to think a double dose gives double protection. The research doesn't support that. In a Spanish study of 2,213 mother-child pairs, mothers who took over 5,000 mcg a day had children who scored about 4 points lower on a test of movement skills.

That's one observational study, and it doesn't mean folic acid is risky. It means stick to the official amount unless your doctor says otherwise. If your doctor has prescribed a higher dose, take it as prescribed. Their reasons are about your history, and the higher dose is part of a plan.

Check that you're not doubling up by accident, too. If you take a prenatal plus a separate folic acid tablet plus a fortified powder, add the numbers.

Food folate, fortified foods and methylfolate

Folate in food is good for you. Leafy greens, beans, lentils and oranges all bring it, and they're worth eating for many reasons. But guidelines ask for the 400 mcg supplement on top of food, because that's what was shown to prevent neural tube defects.

What about methylfolate? It's the active form your body converts folic acid into, and it raises blood folate well. What it hasn't been tested for is the main job: the CDC says no studies show other types of folate prevent neural tube defects. Common MTHFR gene variants are not a reason to avoid folic acid, according to the CDC. If you prefer methylfolate, a product that combines it with the full 400 mcg of folic acid lets you have both. The full debate is in methylfolate vs folic acid.

Folic acid is the start of the plan, not the whole plan. Iodine, iron, vitamin D and choline matter early too. See when to start prenatal vitamins and how to prepare your body for pregnancy.

Go deeper

Grow a Genius

In the book: Chapter 4: Why the Clock Starts Before the Test Turns Positive

Grow a Genius sets folic acid inside a full 90-day countdown, with the questions to ask your doctor about dose and form and a fair, sourced take on the methylfolate debate.

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