Folic Acid Dosing for Pregnancy with Prior Hydrocephalus History
A pregnant woman with a previous pregnancy complicated by hydrocephalus should receive 5000 micrograms (5 mg) of folic acid daily, making option C (5000 micro) the correct answer. 1
High-Risk Classification
Hydrocephalus from a previous pregnancy places this woman in the high-risk category for neural tube defect recurrence, as the Society of Obstetricians and Gynaecologists of Canada specifically includes hydrocephalus in their list of conditions warranting high-dose folic acid supplementation. 1
The American College of Medical Genetics explicitly defines high-risk women as those with a prior pregnancy history of neural tube defects or related conditions, including hydrocephalus. 1
Recommended Dosing Algorithm
High-risk women require 4-5 mg (4000-5000 micrograms) of folic acid daily, starting ideally at least 3 months before conception and continuing through the first 12 weeks of gestation. 1, 2, 3
After 12 weeks of gestation, the dose should be reduced to 0.4-1.0 mg daily for the remainder of pregnancy and 4-6 weeks postpartum or as long as breastfeeding continues. 1, 2
The standard 400 micrograms (option A) is insufficient for women with prior affected pregnancies and is only appropriate for low-risk women without any history of neural tube defects. 1
Evidence Strength and Rationale
The 4-5 mg dose recommendation is based on the landmark British MRC Vitamin Study, which demonstrated that high-dose folic acid supplementation prevents recurrence of neural tube defects. 1
Folic acid supplementation at this dose can prevent 50-72% of neural tube defect recurrences, though not all cases can be prevented due to multifactorial or monogenic etiology. 3
Critical Timing Considerations
Neural tube closure occurs within the first 28 days after conception, often before pregnancy recognition, making preconceptional supplementation essential. 1, 4
Even if the patient is already pregnant, high-dose supplementation should be started immediately, as some protective benefit may still be achieved. 4
Important Safety Considerations
Women requiring doses greater than 1 mg should take additional folic acid-only tablets rather than multiple multivitamin tablets, to avoid excessive intake of other vitamins such as vitamin A. 3, 5
The dose reduction after 12 weeks is crucial to decrease potential health consequences of long-term high-dose folic acid ingestion and mitigate concerns about masking vitamin B12 deficiency-related neurological symptoms. 1, 2
Vitamin B12 deficiency should ideally be ruled out before initiating high-dose folic acid, though investigations are not strictly required if the patient is taking a multivitamin containing 2.6 μg/day of vitamin B12. 4, 3