Folic Acid Dosing for Primigravida with Family History of Neural Tube Defect
A primigravida with a cousin who had anencephaly should take 400-800 micrograms (0.4-0.8 mg) of folic acid daily, which corresponds to option A (1000 micrograms is acceptable but slightly higher than standard). This woman does not meet criteria for high-risk dosing because a cousin represents a third-degree relative, which does not constitute high-risk status requiring 4-5 mg daily. 1, 2
Risk Stratification Algorithm
Standard Risk (400-800 μg daily):
- Women without personal history of NTD-affected pregnancy 1, 2
- Women without first- or second-degree relatives with NTDs 1, 2
- Women not taking high-risk medications (antiepileptic drugs, particularly valproic acid or carbamazepine) 1, 3
- Women without type 1 diabetes mellitus 1
High Risk (4,000-5,000 μg daily):
- Personal history of NTD-affected pregnancy 1, 4, 3
- First- or second-degree relative with NTD 1, 3
- Taking antiepileptic medications during early pregnancy 1, 5, 3
- Type 1 diabetes mellitus 1
- Obesity 1
Why This Patient is Standard Risk
A cousin represents a third-degree relative, and the American College of Medical Genetics specifies that high-risk status requires a first-, second-, or third-degree relative with NTD; however, the preponderance of guideline evidence emphasizes first- and second-degree relatives as the primary high-risk criteria. 2, 3
The most recent and authoritative guideline (2025) explicitly states that "a family history of neural tube defects in a cousin does not constitute high risk." 2
Practical Implementation
All women of reproductive age should take folic acid supplementation continuously, as more than 50% of pregnancies are unplanned and neural tube closure occurs within the first 28 days after conception, often before pregnancy recognition. 1, 2
The supplementation should begin immediately and continue at least 2-3 months before conception through the first trimester. 1, 3
Standard-dose folic acid (400-800 μg) can be obtained through over-the-counter multivitamins, fortified breakfast cereals, and enriched grain products, in addition to a folate-rich diet. 2
Critical Safety Considerations
Total daily folic acid intake should remain below 1 mg unless under physician supervision, as doses exceeding 1 mg may mask vitamin B12 deficiency, potentially leading to irreversible neurologic damage. 2
At the standard dose of 400-800 μg, vitamin B12 screening is not required before initiating supplementation, as this dose is safe and well-tolerated. 2
High-dose folic acid (4-5 mg) should only be prescribed as a single prescription-strength tablet, not multiple multivitamins, to avoid excessive intake of other vitamins such as vitamin A, which is teratogenic. 1
Common Pitfall to Avoid
Do not automatically prescribe high-dose folic acid (4-5 mg) for all family history of NTDs—carefully assess the degree of relationship. Third-degree relatives (cousins) do not warrant high-dose supplementation according to current guidelines. 2
If this patient had a first-degree relative (parent, sibling, or child) or second-degree relative (aunt, uncle, niece, nephew, grandparent) with an NTD, then 4,000-5,000 μg daily would be indicated. 1, 3