All pregnant women – and women who are trying to get pregnant – should take a daily folic-acid supplement until the end of their 12th week of pregnancy.¹ But the recommended amount of folic acid you should take does vary according to your weight. Here's how – and why...


The takeaway expert advice

The standard daily dose of folic-acid in pregnancy is 400 micrograms (mcg).¹ But, if you're pregnant and your BMI (body mass index) is over 30, you'll need to take a bigger dose of 5 milligrams (mg) of folic acid a day.²

This bigger 5mg dose will need to be prescribed by a doctor.

Why do you need to take more folic acid if you have obesity?

Folic acid decreases the risk of your baby having neural tube defects, such as spina bifida (an issue with the development of the spine and brain).

Neural tube defects are rare but, if you have obesity (a BMI over 30), you are at an increased risk of having a pregnancy affected by a neural tube defect.3,4

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So, the increased folic acid dose is recommended to help decrease this risk.

Do I need to see my doctor about this? Can't I just increase the number of regular tablets I take?

You would need to take 12.5 tablets of the 400mcg dose every day to reach your recommend 5mg dose – which is a lot of tablets and a lot of counting!

Plus, most regular 400mcg folic-acid supplement are sold over the counter, so the cost of 12.5 of them a day would rapidly add up.

Your doctor can prescribe you 5mg tablets of folic acid which will be much easier to take daily – and, as prescriptions are free if you are pregnant, this will save you money.

What if I haven't taken any – or enough – folic-acid tablets yet?

Ideally, you should start taking it a month before you conceive, and keep taking it up to the end of your 12th week of pregnancy.

But, if you have obesity and you haven't taken the bigger dose yet or you didn't take any folic acid before you found out you're pregnant, starting to take it now can still help.


1. Vitamins, supplements and nutrition in pregnancy. NHS Online
2. Being overweight in pregnancy and after birth. Royal College of Obstetricians & Gynaecologists, Nov 2018 (updated Aug 2022).
3. Does Obesity Increase the Risk of Having a Child With a Birth Defect? Tinker S. C. and Cragan J. D. Teratology Primer, 3rd ed.
4. Obesity, Neutral Tube Defects and Folic Acid — A Complex Relationship. Koren G. and Kaplan Y. C. Clin. Exp. Obstet. Gynecol. 2021, 48(2), 223–227.

Pic: Getty Images


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Dr Philippa Kaye works as a GP in both NHS and private practice. She attended Downing College, Cambridge, then took medical studies at Guy’s, King’s and St Thomas’s medical schools in London, training in paediatrics, gynaecology, care of the elderly, acute medicine, psychiatry and general practice.