Folic Acid (Pre-conception and Pregnancy)

How it works

Folic acid is converted to tetrahydrofolate, an essential cofactor for nucleotide synthesis and methylation reactions required for rapid cell division and closure of the neural tube in early embryonic development.

Prescribing in practice

• Supplementation should ideally begin before conception and continue through the first trimester, as the neural tube closes early in pregnancy, before many women know they are pregnant.
• A higher-strength preparation is indicated for women at increased risk, including those with a previous affected pregnancy, diabetes, a high body-mass index, sickle cell disease, or taking antiepileptic or other antifolate medicines.
• Folic acid can mask the haematological signs of vitamin B12 deficiency while allowing neurological damage to progress, so consider B12 status where deficiency is plausible.

Monitoring

Routine biochemical monitoring is not required for standard antenatal supplementation, the focus being on timely initiation and adherence.

Counselling the patient

• Start taking folic acid as soon as you plan a pregnancy, not when you first miss a period.
• Continue daily through the early weeks of pregnancy even if you feel well.
• Tell your clinician if you have epilepsy, diabetes or a previous pregnancy affected by spina bifida, as you may need a stronger dose.

Evidence & guidelines

The landmark MRC Vitamin Study and subsequent guidance established that periconceptional folic acid substantially reduces the risk and recurrence of neural tube defects.