folic acid and prophylaxis against neural tube defects

Last edited 06/2022

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 recurrence

    • also dose recommended for women who are:
      • receiving anti-epileptic medication (1) or

      • who have diabetes (2) or

      • who have sickle cell disease (3) or

      • women with a BMI of 30 kg/m2 or greater *(4)

  • folic acid 400 mcg daily to prevent first occurence

* women with a BMI 30 kg/m2 or greater wishing to become pregnant should be advised to take 5 mg folic acid supplementation daily, starting at least 1 month before conception and continuing during the first trimester of pregnancy

Folic acid should be commenced prior to conception and continued for the first trimester.

A review states (5)

  • 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, body mass index >= 30, 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
    • is a lack 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


  • pregnant women (and those intending to become pregnant) should be informed that dietary supplementation with folic acid, before conception and up to 12 weeks-gestation, reduces the risk of having a baby with neural tube defects (anencephaly, spina bifida). The recommended dose is 400 micrograms per day (1)