Following the first reports that taking folic acid reduced risk
for neural tube defects, the California Birth Defects Monitoring
Program pioneered research looking at folic acid use in a variety
of birth defects.
Folic acid is a B vitamin used by cells as they grow and
divide. The naturally occurring form, folate, is found in
spinach and leafy green vegetables, dried beans, liver and
citrus fruits. Folic acid is also found in fortified foods
such as breakfast cereal. It is estimated that diet supplies
the average woman only about 0.2 milligrams of folate daily
(about half the recommended amount).
Because dietary sources are often inadequate, research concentrates
on women's use of multivitamin supplements containing folic
acid. Our studies look at vitamin use around the time of
conception
and in early pregnancy—the critical period for fetal development.
PROTECTIVE EFFECT SEEN FOR MANY CONDITIONS
Our studies showed reduced risk for many types of birth defects
in mothers taking multivitamins containing folic acid around
the time of conception. Among women who did not take multivitamins,
those consuming fortified cereal daily also had lower risk.
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Neural tube defects: 35% lower risk, but
college-educated women and Latina mothers had much less
benefit than other groups. 
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Oral clefts: 25%-50% risk reduction, depending on type
of cleft.
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Heart defects: 30% risk reduction for conotruncal
heart defects.
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Limb defects: 36% lower risk for reduction-type defects,
particularly longitudinal defects (those affecting a lengthwise
segment of the arm/leg). There was no effect for transverse
(amputation-type) defects.
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Multiple birth defects: about a 60% risk reduction.
No particular organ system was uniquely affected by multivitamin
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GENES AND FOLIC ACID METABOLISM
Taking vitamins does not eliminate the risk for birth defects-why
do some pregnancies benefit while others do not? The search
to understand how supplementation alters risk has focused
on a number of genes that influence the developing baby's
folic acid metabolism. Variant forms of these genes can lower
folic acid levels, particularly if the mother does not take
multivitamins containing folic acid. We determined which babies
inherited double doses of variant genes and whose mothers
did not use multivitamins, and found:
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MTHFR: About 1 in 6 babies has the genetic
type "TT" of methylenetetrahydrofolate reductase
(MTHFR); this variant is more common in Latino infants.
Babies with type "TT" had a modest increase
in neural tube defect risk. Their risk for oral clefts
was not affected.
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TGF :
If their mothers did not take multivitamins, infants with
the less common A2 form of the transforming growth factor-alpha
(TGF)
gene were at 2-8 times higher risk, depending on the type
of cleft. |
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