What is the recommended dose of folic acid (Vitamin B9) for pregnant women?

Folic Acid Requirements During Pregnancy

All women capable of becoming pregnant should take 400 μg (0.4 mg) of folic acid daily, with higher doses of 4 mg daily recommended for high-risk women starting at least 3 months before conception through the first 12 weeks of pregnancy. 1, 2

General Recommendations

For Low-Risk Women:

• Dosage: 400-800 μg (0.4-0.8 mg) daily 1, 2
• Timing: Start at least 1 month before conception, preferably 3 months before, and continue through at least the first trimester 1
• Sources: Supplements, multivitamins, fortified foods, or a combination 1

For High-Risk Women:

• Dosage: 4 mg (4000 μg) daily 1, 2
• Timing: Start at least 3 months before conception and continue until 12 weeks gestation, then reduce to 400 μg daily 1
• Who qualifies as high-risk:
  • Personal history of neural tube defects
  • Previous pregnancy affected by neural tube defects
  • First or second-degree relative with neural tube defect
  • Type 1 diabetes mellitus
  • Exposure to certain medications (anticonvulsants like valproic acid or carbamazepine) 1, 2

Clinical Considerations

Rationale for Supplementation

• Neural tube closure occurs within the first 28 days after conception, often before pregnancy recognition 2
• Folic acid supplementation can prevent 40-80% of neural tube defects 1
• Even with food fortification, supplementation provides additional protection 1

Safety Considerations

• Daily doses exceeding 1 mg are not recommended unless medically indicated, as they may mask vitamin B12 deficiency 1, 3
• Folic acid is water-soluble and excess is rapidly excreted 1
• For women on higher doses (4 mg), it's recommended to reduce to 400 μg after 12 weeks gestation 1

Special Situations

• Women taking medications that interfere with folate metabolism (anticonvulsants, methotrexate, sulfasalazine) may require higher doses 2
• Women with severe malabsorption conditions may need higher doses 2
• Patients on chronic hemodialysis may require 1-5 mg daily 2

Maintenance After First Trimester

• After 12 weeks gestation, women who were on 4 mg should reduce to 400-800 μg daily 1, 2
• Continuation of 400 μg throughout pregnancy is recommended to meet fetal growth and developmental needs 1
• Some evidence suggests continued supplementation in the second and third trimesters can maintain maternal folate status and prevent increases in homocysteine 4

Common Pitfalls

1. Delayed initiation: Many women start supplementation after conception, missing the critical period for neural tube development
2. Inadequate dosing for high-risk women: Failure to prescribe 4 mg for women with risk factors
3. Poor compliance: Studies show fewer than 1 in 3 women consume the recommended amount of folic acid
4. Overreliance on diet alone: Food folates are about half as bioavailable as synthetic folic acid, making supplementation necessary 1
5. Failure to identify high-risk women: Not recognizing risk factors that warrant higher dosing

Despite appropriate supplementation, it's important to note that not all neural tube defects can be prevented due to their multifactorial etiology 1. However, proper folic acid supplementation remains one of the most effective preventive measures available for reducing the risk of these serious birth defects.