Recommended Folic Acid Dosing
All women of reproductive age should take 400-800 μg (0.4-0.8 mg) of folic acid daily, while high-risk women require 4,000 μg (4 mg) daily starting at least 3 months before conception through the first 12 weeks of pregnancy, then reducing to 400 μg for the remainder of pregnancy. 1, 2, 3
Standard Dosing for Average-Risk Women
For typical adult women capable of becoming pregnant:
- Take 400-800 μg (0.4-0.8 mg) daily starting at least 1 month before conception and continuing through the first trimester 1, 4
- After 12 weeks gestation, continue 400 μg (0.4 mg) daily throughout the remainder of pregnancy to support fetal growth and development 2, 3
- This universal recommendation applies because approximately 50% of U.S. pregnancies are unplanned, and neural tube closure occurs within the first 28 days after conception—often before pregnancy recognition 1, 3
The evidence supporting this dose is robust: The USPSTF issued a Grade A recommendation (highest level) with high certainty that the net benefit is substantial, based on convincing evidence from randomized trials and observational studies 1, 4. Multiple international health organizations and WHO endorse this 400 μg daily dose 5.
High-Risk Women: Critical 10-Fold Dose Increase
High-risk women require 4,000 μg (4 mg) daily—not the standard 400 μg dose. 1, 3, 6
High-risk criteria include:
- Prior pregnancy affected by neural tube defect 1, 3, 6
- Personal history of neural tube defect 3, 6
- First-degree relative with neural tube defect 1, 6
- Type 1 diabetes mellitus 2, 3
- Taking certain antiseizure medications 1, 2
Specific high-risk dosing protocol:
- Start 4,000 μg (4 mg) daily at least 3 months (12 weeks) before conception—earlier than the standard recommendation 3, 6
- Continue 4,000 μg (4 mg) daily through the first 12 weeks of gestation 3, 6
- After 12 weeks, reduce to 400 μg (0.4 mg) daily for the remainder of pregnancy—this reduction is crucial to minimize long-term risks of high-dose supplementation, particularly masking vitamin B12 deficiency 2, 3, 6
This 4 mg dose is based on the landmark British MRC Vitamin Study, which demonstrated prevention of neural tube defect recurrence 1, 3, 6. The American College of Medical Genetics and CDC specifically endorse this high-risk dosing 1, 7.
Critical Safety Ceiling
Total daily folate consumption should not exceed 1,000 μg (1 mg) unless prescribed by a physician. 1, 2, 3
- Doses exceeding 1 mg daily may mask vitamin B12 deficiency, allowing irreversible neurological damage to progress while correcting the hematologic manifestations 1, 2, 3
- Always rule out vitamin B12 deficiency before initiating high-dose folic acid supplementation 3
- The FDA label confirms that daily doses greater than 1 mg do not enhance hematologic effects, with excess excreted unchanged in urine 8
Common Pitfalls to Avoid
Do not prescribe 4 mg to average-risk women: A Cochrane meta-analysis confirmed that higher doses (>400 μg) in average-risk women provide no additional benefit for preventing neural tube defects or other birth defects 3. This only increases the risk of masking B12 deficiency without improving outcomes 3.
Do not stop supplementation after 12 weeks in average-risk women: Continue 400 μg daily throughout pregnancy for ongoing fetal growth needs, not just neural tube defect prevention 2, 3.
Do not continue 4 mg beyond 12 weeks in high-risk women: The dose reduction after the first trimester is essential to minimize long-term high-dose risks 2, 3, 6.
Do not rely on diet alone: While food fortification has reduced spina bifida rates by 31% in the U.S., dietary folate is only half as bioavailable as synthetic folic acid, and most women do not consume fortified foods at levels providing optimal benefit 1. Supplementation remains essential 1, 7.