What is the recommended dose of folic acid (Vitamin B9) in pregnancy?

Folic Acid Dosing in Pregnancy

All women of childbearing age should take 400-800 μg (0.4-0.8 mg) of folic acid daily, starting at least 1 month before conception and continuing throughout pregnancy, with high-risk women requiring 4 mg daily starting 3 months preconception until 12 weeks gestation. 1

Standard Dose for Average-Risk Women

The recommended dose is 400-800 μg (0.4-0.8 mg) daily for all women capable of becoming pregnant. 1 This recommendation is supported by:

• The US Preventive Services Task Force (USPSTF) reaffirmed in 2017 that 400-800 μg daily provides substantial net benefit with high certainty 1
• The American College of Medical Genetics (ACMG) recommends 400 μg (0.4 mg) daily for all women of childbearing age 1
• This dose should begin at least 1-4 weeks before planned conception and continue through the first trimester 1

After 12 weeks gestation, continue 400 μg (0.4 mg) daily throughout the remainder of pregnancy to meet fetal growth and developmental needs, even though neural tube protection is complete by this point. 1, 2

Critical Timing Considerations

• Since approximately 50% of pregnancies are unplanned, continuous supplementation is recommended for all reproductive-age women, not just those actively planning pregnancy 1, 3
• Maximal protection requires starting supplementation before conception, as neural tube closure occurs by 28 days post-conception 1

High-Risk Women: 4 mg Daily Protocol

Women at high risk require 4,000 μg (4 mg) daily starting at least 3 months before conception and continuing until 12 weeks gestation. 1 After 12 weeks, reduce to the standard 400 μg (0.4 mg) daily dose. 1, 2

High-Risk Criteria Include:

• Previous pregnancy affected by neural tube defect 1, 3
• Personal history of neural tube defect 1, 3
• First- or second-degree relative with neural tube defect 1, 3
• Partner with personal history of neural tube defect 3
• Type 1 diabetes mellitus 1
• Type 2 diabetes or BMI >30 kg/m² 3
• Exposure to certain antiseizure medications (valproic acid, carbamazepine) 1

Rationale for Dose Reduction After 12 Weeks

Reducing from 4 mg to 400 μg after 12 weeks gestation decreases the risk of masking vitamin B12 deficiency-related neurological symptoms while maintaining adequate folate for fetal development. 1, 2 This timing corresponds with completion of major organ development, including neural tube closure. 1

Safety Considerations and Upper Limits

Total daily folic acid intake should not exceed 1 mg (1000 μg) unless specifically prescribed for high-risk conditions. 3, 2 Key safety points:

• Higher doses may mask vitamin B12 deficiency, potentially leading to irreversible neurological damage if left undiagnosed and untreated 2, 4
• Doses greater than 1 mg do not enhance hematologic effects, and excess is excreted unchanged in urine 4
• The Cochrane meta-analysis found that doses >400 μg provide no additional benefit for preventing neural tube defects or other birth defects in average-risk women 1

Evidence Quality and Effectiveness

Folic acid supplementation reduces neural tube defects by 40-80% when taken periconceptionally. 3, 5 The evidence base includes:

• Multiple randomized controlled trials demonstrating efficacy 5, 6
• Post-fortification surveillance showing 20% reduction in spina bifida rates in the U.S. after mandatory food fortification 6
• USPSTF Grade A recommendation (highest level of certainty) for the 400-800 μg dose 1

Important Limitations

Even with adequate supplementation, not all neural tube defects can be prevented due to multifactorial and monogenic etiologies. 1, 2 Some cases are folate-resistant and may require alternative approaches such as myo-inositol supplementation. 1

Practical Implementation

Supplementation should be combined with consumption of folate-rich foods and fortified products, though dietary sources alone are insufficient to meet recommended levels. 1 The USPSTF acknowledges that most women cannot consume adequate folic acid from food alone despite access to fortified products. 1

Common Pitfall to Avoid

Do not delay supplementation until pregnancy is confirmed—neural tube closure occurs by 28 days post-conception, often before women know they are pregnant. 1 This is why universal supplementation for all reproductive-age women is recommended rather than waiting until pregnancy planning begins. 1, 3