This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (firstname.lastname@example.org) with numerous contributions by others.
2.e Folic acid (or folacin) is a vitamin found in green vegetables, legumes
and other sources. An average diet is generally deficient in folic acid.
Studies have shown that when women with known risk factors of having a baby
with neural tube defects take folic acid supplements from before conception
to about 8 weeks of pregnancy, they can reduce their risk for these
defects. A more recent study claims that this is beneficial for all women,
not just those with previous risk factors.
For pregnant women or those trying to get pregnant, the recommended daily
amount of folic acid is either 400 or 800 micrograms (.4 or .8 mgs)
depending on what source you read. It is very unwise to take more than a
1000 micrograms (1 mg) a day, as folic acid at this level can mask other
serious health problems. In fact, because of this caution, in some places
folic acid is not sold over the counter as a stand alone supplement. This
may be changing due to this new link to neural tube defects. I was able to
find 800 mcg folic acid capsules over the counter in Washington state.
Someone from Pennsylvania reports that it is not available there except by
prescription. All prenatal vitamins ought to have at least 400 mcg. The FDA
is also considering requiring fortification of grain products with folacin.
While the benefit of taking folic acid on neural tube defects is limited to
early in pregnancy, it is still an important nutrient for building red
blood cells and is important throughout the entire pregnancy. Some doctors
are beginning to consider it as important as iron supplementation. Talk to
your dr for his or her recommendation.