Folic Acid Dosing for Preconception
All women of childbearing age planning to conceive should take 400-800 μg (0.4-0.8 mg) of folic acid daily, starting at least 4 weeks before planned conception and continuing through the first trimester. 1
Standard Dosing for Average-Risk Women
Take 400-800 μg (0.4-0.8 mg) daily beginning at least one month before conception and continuing through 12 weeks of gestation. 1, 2, 3
This recommendation is endorsed by the US Preventive Services Task Force, American College of Medical Genetics and Genomics, and multiple other organizations with high certainty of substantial net benefit. 1, 3
After 12 weeks gestation, continue 400 μg (0.4 mg) daily throughout the remainder of pregnancy to meet fetal growth and developmental needs. 2
This universal recommendation applies to all women capable of becoming pregnant because approximately 50% of pregnancies are unplanned, and neural tube closure occurs within the first 28 days after conception—often before pregnancy recognition. 2, 4
Supplementation can prevent 50-70% of neural tube defects such as spina bifida and anencephaly. 5, 4
High-Risk Women: Critical Dosing Differences
High-risk women require 4,000-5,000 μg (4-5 mg) daily—a 10-fold higher dose than standard supplementation. 1, 6, 2
Who Qualifies as High-Risk:
- Personal history of neural tube defect 1
- Prior pregnancy affected by neural tube defect 1, 5
- First or second-degree relative with neural tube defect 1, 6
- Type 1 diabetes mellitus 1
- Taking antiepileptic medications (e.g., valproic acid, carbamazepine, lamotrigine) 1, 6
- Partner or prior offspring with neural tube defect 1
High-Risk Dosing Algorithm:
Start 4,000-5,000 μg (4-5 mg) daily at least 12 weeks (3 months) before conception—this earlier start reflects the need for adequate tissue saturation. 1, 6, 2
Continue 4,000-5,000 μg (4-5 mg) daily through the first 12 weeks of gestation until completion of major organ development. 1, 6, 2
After 12 weeks gestation, reduce to 400 μg (0.4 mg) daily for the remainder of pregnancy—this dose reduction is crucial to decrease potential health consequences of long-term high-dose ingestion, particularly masking vitamin B12 deficiency-related neurological symptoms. 1, 6, 2
For women with a prior neural tube defect-affected pregnancy specifically, the Centers for Disease Control and Prevention recommends 4,000 μg daily beginning at least 1 month before conception. 5
Critical Safety Considerations
Always rule out vitamin B12 deficiency before initiating high-dose folic acid (>1 mg), as folate can correct the hematologic manifestations of B12 deficiency while allowing irreversible neurological damage to progress. 6, 2
Total daily folate consumption should not exceed 1,000 μg (1 mg) unless prescribed by a physician for high-risk conditions. 2, 7
Doses greater than 1 mg do not enhance the hematologic effect in most patients, and most excess is excreted unchanged in the urine. 7
Common Pitfalls to Avoid
Do not prescribe 4-5 mg to average-risk women—higher doses provide no additional benefit for preventing neural tube defects or other birth defects (cleft lip/palate, congenital heart defects, miscarriages) and increase the risk of masking B12 deficiency. 1, 2
Do not stop supplementation after 12 weeks in average-risk women—continue 400 μg daily throughout pregnancy for fetal growth needs. 2
Do not continue 4-5 mg beyond 12 weeks gestation in high-risk women—reduce to 400 μg to minimize long-term high-dose risks. 1, 6, 2
Do not delay starting supplementation—neural tube defects occur before pregnancy recognition in most cases, making preconception supplementation essential. 2, 8
Important Limitations
Even with adequate folic acid supplementation, not all neural tube defects can be prevented due to their multifactorial or monogenic etiology. 1, 6