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More Evidence that Pregnant Women Need Folic Acid

By Cheryl Simon Silver

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A joint study by researchers in the United States and Ireland shows that far more people are at increased risk for having a neural tube defect such as spina bifida than scientists had previously realized. The finding underscores the idea that women of childbearing age should take supplements of folic acid, which lower the risk of this type of birth defect.

It had been thought that only children with two copies of a particular gene variant were at increased risk for the neural tube defects that can affect the brain and spinal cord.

But when the researchers tested DNA of people with and without a neural tube defect, they found that individuals with one copy of the gene were 1.5 times as likely to have a neural tube defect as a person without a single copy of the gene. Individuals with two copies of the gene—one from each parent—were 2.5 times as likely to have a neural tube defect.

About 60 percent of Europeans and 50 percent of North Americans carry either one or two copies of the gene variant, known as C677T. The incidence of neural tube defects is about seven in 10,000 pregnancies.

The finding lends new urgency to the ongoing recommendation that all women of childbearing age take 400 micrograms of the vitamin folic acid each day. For unknown reasons, folic acid, the synthetic form of the vitamin folate, cuts in half a woman’s chances of giving birth to a child with a neural tube defect.

“The importance of this study is that now we know there is a much larger population at risk for neural tube defects,” says James Mills, of the National Institute of Child Health and Human Development (NICHD) in Rockville, Maryland, and an author of the study. “This is a defect that can almost certainly be overcome by taking folic acid prior to conception.”

The neural tube develops during the first four weeks after conception, and most women do not know they are pregnant until after the fetus has passed through this critical stage.

Because the majority of pregnancies in the United States are unplanned, the government since 1992 has urged all women of childbearing age to take supplemental folic acid. In 1998, the U.S. Food and Drug Administration initiated its requirement that folic acid be added to the grain supply.

The gene can be carried by either parent. It cannot be used as a prenatal genetic test because not all babies with the gene are born with a neural tube defect, Mills says.

The study, done by scientists in the United States and Ireland, drew its subjects from Ireland because that country has a high proportion of individuals with neural tube defects. The researchers tested 395 individuals with a neural tube defect and 848 who did not have such a defect.

The findings appear in the online version of the British Medical Journal. Peadar Kirke of the Health Research Division in Dublin, Ireland, led the study.

Scott, John M. et al. Impact of the MTHFR C677T polymorphism on risk of neural tube defects: case-control study. British Medical Journal 328, 1535-1536 (June 26, 2004).

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