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Vitamin / Neural Tube Defect Prevention Pregnancy: Indicated in pregnancy — standard pre-conception and first trimester care

Folic Acid (Pre-conception and Pregnancy)

Brand names: Preconceive, Lexpec (5mg)

Adult dose

Dose: Standard risk: 400 mcg (0.4 mg) daily. High risk: 5 mg daily. Start before conception and continue until 12 weeks gestation
Route: Oral
Frequency: Once daily
Max: 5 mg/day (high-risk groups)
High-risk indications for 5 mg dose: previous NTD pregnancy, diabetes mellitus, antiepileptic drug use (valproate, carbamazepine), BMI >30, malabsorption, family history of NTD. NICE recommends supplementation from pre-conception to 12 weeks.

Paediatric dose

Route: N/A
Frequency: N/A
Max: N/A
Not applicable in obstetric indication

Dose adjustments

Renal

No dose adjustment required

Hepatic

No dose adjustment required

Clinical pearls

  • Reduces risk of neural tube defects (spina bifida, anencephaly) by 70% if started pre-conception
  • 5 mg dose for high-risk women: type 1 or 2 diabetes, previous NTD baby, antiepileptic use, BMI >30, malabsorption syndromes
  • Often continued beyond 12 weeks in women with haematological conditions or antiepileptic drug use
  • Available OTC (400 mcg) — prescribe 5 mg on FP10 for high-risk women
  • Folic acid is NOT folate — but the terms are used interchangeably clinically

Contraindications

  • Undiagnosed anaemia (folic acid may mask vitamin B12 deficiency — correct B12 first)

Side effects

  • Generally very well tolerated
  • Rare: GI disturbance
  • May mask pernicious anaemia (B12 deficiency) if given alone

Interactions

  • Antiepileptics (phenytoin, carbamazepine, valproate) — reduced folic acid levels; 5 mg dose required
  • Methotrexate — folic acid reduces GI side effects but may slightly reduce efficacy (not used in MTX ectopic protocol)
  • Sulfasalazine — impairs folate absorption

Monitoring

  • No routine monitoring required for standard dose
  • FBC in at-risk women (haematological conditions)
  • B12 levels before starting if deficiency suspected

Reference: BNFc; NICE NG3 Antenatal Care; NICE NG133; PHE Folic Acid Guidance; BNF. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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