Folic Acid Supplementation in Pregnancy
All women of reproductive age who are capable of becoming pregnant should take 400-800 μg (0.4-0.8 mg) of folic acid daily, starting at least 1 month before conception and continuing through the first 12 weeks of pregnancy. 1
Standard Dosing for Average-Risk Women
- Women at low risk require 400-800 μg (0.4-0.8 mg) of folic acid daily through supplements or fortified foods, in addition to a folate-rich diet 1, 2
- Supplementation must begin at least 1 month before conception (ideally 2-3 months) and continue through the first trimester for maximal neural tube defect prevention 1
- After 12 weeks gestation, continue 400 μg (0.4 mg) daily as part of prenatal vitamins throughout pregnancy and 4-6 weeks postpartum or while breastfeeding to support fetal growth and maternal needs 1, 2
Critical timing consideration: Since approximately 50% of pregnancies in the United States are unplanned, all women of reproductive age (12-45 years) should take folic acid supplementation regardless of pregnancy plans 1. This universal recommendation exists because the neural tube closes by 28 days after conception—often before a woman knows she is pregnant 3.
High-Risk Dosing
Women at high risk require 4 mg (4,000 μg) of folic acid daily, which is 10 times the standard dose 1, 4:
High-risk criteria include:
- Personal history of neural tube defect 1
- Previous pregnancy affected by neural tube defect 1
- First-degree relative (parent, sibling, child) with neural tube defect 1, 4
- Use of certain antiseizure medications (valproic acid, carbamazepine) 1, 2
- Male partner with personal history of neural tube defect 4
High-risk dosing protocol:
- Begin 4 mg daily at least 3 months before conception (not just 1 month) 1, 4
- Continue through 12 weeks gestation 1, 4
- After 12 weeks, reduce to standard dose of 400-1,000 μg (0.4-1.0 mg) daily for remainder of pregnancy 1, 4
Important safety note: Women requiring doses above 1 mg should take one multivitamin tablet plus additional folic acid-only tablets to reach the target dose—never multiple multivitamin tablets, as this risks vitamin toxicity from other components 4.
Moderate-Risk Dosing
Women with moderate risk factors require 1 mg (1,000 μg) daily 4:
Moderate-risk criteria include:
Moderate-risk protocol:
- Begin 1 mg daily at least 3 months before conception 4
- Continue through 12 weeks gestation 4
- After 12 weeks, may continue 400-1,000 μg daily through pregnancy and postpartum 4
Safety Considerations and Common Pitfalls
The upper limit for folic acid is 1,000 μg (1 mg) daily for average-risk women due to theoretical concerns about masking vitamin B12 deficiency 1, 2. However, this concern is largely theoretical—investigations for B12 deficiency are not required before starting folic acid supplementation 4. Taking folic acid in a multivitamin containing 2.6 μg/day of vitamin B12 mitigates even these theoretical concerns 4.
Key clinical pearls:
- Folic acid from supplements is better absorbed than food folate (pteroylpolyglutamic acid), making supplementation essential even with a folate-rich diet 5, 4
- Women with prior neural tube defect-affected pregnancies may have diminished folate absorption and require higher doses 5
- Even with adequate supplementation, not all neural tube defects can be prevented due to multifactorial etiology 1
- Doses above 1 mg do not enhance hematologic effects in most patients, and excess is excreted in urine 6
Evidence Quality and Guideline Consensus
The U.S. Preventive Services Task Force found convincing evidence with high certainty that folic acid supplementation provides substantial net benefit for neural tube defect prevention, with no serious harms at recommended doses 1. This represents Grade A evidence—the highest level of recommendation 1. The American College of Medical Genetics, American Academy of Pediatrics, and multiple international organizations endorse these same dosing recommendations 1, 7.