Neural tube defects such as spina bifida and anencephaly affect 1 in 1,000 newborns in the US. If you were planning a trip by automobile or airplane and were told there was a 1 in 1,000 chance you would not arrive safely, would you still take the trip?
Such risks are usually not a topic of discussion for most couples contemplating pregnancy. It has been known since the 1980s, however, that the use of supplemental folic acid before pregnancy can significantly reduce the likelihood of neural tube defects, even though women with an affected infant show no evidence of clinical folic acid deficiency. Neural tube defects appear to result from a folic acid receptor blockade by maternal autoantibodies.1 Supplemental, but not dietary, folic acid is able to free up the receptors so that normal embryonic nerve tissue development ensues. Unfortunately, introduction of supplemental folic acid after conception has no apparent neuroprotective effect.
In the UK, where the incidence of neural tube defects is greater than in the US, physicians have advised that in addition to consuming flour and grain products fortified with folic acid, women should take 4000 micrograms of folic acid daily when attempting pregnancy or exposed to pregnancy without contraception.2 The recommended 4000 mcg dose of folic acid has been shown to prevent 83% of neural tube defects, compared to only a 36% reduction with the standard 400 microgram dose of multivitamins.
Based on the current study and applying a dose-response model,3 it is now recommended that women take 5000 micrograms of folic acid during the preconception period and first trimester to maximally reduce the risk of neural tube defects. At least 1000 micrograms of vitamin B12 should also be consumed daily to guard against pernicious anemia.
—Dean S. Cunningham, MD, PhD