Folic acid supplements at the time of conception helps to prevent neural tube defects. The dose of folic acid recommended for women hoping to conceive is:
- folic acid 5mg daily
- to prevent the recurrence of neural tube defects
- also offer a high-dose folic acid supplement (5 mg a day) to anyone who is planning to become pregnant or is in the first 12 weeks of pregnancy if they have an increased risk of having a baby with a neural tube defect or other congenital malformation, for example, if they (1,2):
- (or their partner) have, or if there is a family history of, a neural tube defect or other congenital malformation
- have had a previous pregnancy affected by a neural tube defect or other congenital malformation
- have type 1 or type 2 diabetes
- have a haematological condition that requires folic acid supplementation, such as sickle cell anaemia or thalassaemia
- folic acid 400 mcg daily to prevent first occurrence
With respect to folic acid supplementation and obesity:
- reassure anyone with a body mass index (BMI) of 25 kg/m2 or more who is planning to become pregnant or is in the first 12 weeks of pregnancy that they do not need to take more than 400 micrograms of folic acid a day, unless they have any of the factors listed for use of folic acid 5mg daily (2)
- note that recommendations for high dose intake in this population are not supported by robust evidence, and it is likely that the higher incidence of neural tube defects in this group might not be due to folate insufficiency but potentially unrelated metabolic factors (1)
With respect to folic acid supplementation and previous bariatric surgery:
- if a person has had bariatric surgery and is planning a pregnancy or is pregnant, advise them to contact their bariatric surgery unit for individualised, specialist advice about folic acid and other micronutrients
Folic acid should be commenced prior to conception and continued for the first trimester.
A review states (3):
- taking a supplement with 0.4 mg per day (standard dose) of folic acid at least 3 months before pregnancy until the 12th week of pregnancy helps prevent neural tube defects for most individuals
- guidelines recommend 0.4 mg of folic acid per day in the periconceptional period, and certain guidelines recommend high doses (4-5 mg/day) in women at higher risk for neural tube defects such as those with diabetes, or taking antiepileptic medications or other folate antagonists
- for those who had a previous pregnancy affected by neural tube defect, high-quality evidence from a large randomised clinical trial supports using 4 mg per day of folic acid
- there is a lack of evidence to suggest that high doses have additional benefit in preventing neural tube defects in women with other risk factors
- folic acid supplements should be taken in addition to consuming a folate-rich diet because diet alone does not provide maximal protection against neural tube defects
- folic acid doses of 4-5 mg per day have not been associated with any side effects or harms, but there is limited evidence on this
Note:
- pregnant women (and those intending to become pregnant) should be informed that dietary supplementation with folic acid, before conception and up to 12 weeks of gestation, reduces the risk of having a baby with neural tube defects (anencephaly, spina bifida). The recommended dose is 400 micrograms per day (1).
References:
- Deshpande S, Ross S, Rajesh S, Kallioinen M. Maternal and child nutrition: nutrition and weight management in pregnancy, and nutrition in children up to 5 years - summary of new NICE guidance. BMJ 2025; 389:r954.
- NICE (January 2025). Maternal and child nutrition: nutrition and weight management in pregnancy, and nutrition in children up to 5 years.
- Dwyer E R, Filion K B, MacFarlane A J, Platt R W, Mehrabadi A. Who should consume high-dose folic acid supplements before and during early pregnancy for the prevention of neural tube defects? BMJ 2022; 377:e067728 doi:10.1136/bmj-2021-067728.