A study of almost 250,000 women conducted by the federal government and released Thursday provides compelling evidence that pregnant women taking the vitamin folic acid to prevent birth defects are not at an increased risk of giving birth to twins.

ATLANTA, Jan. 30, 2003

Although folic acid is known to prevent birth defects affecting the brain and spinal cord, there was some concern from previous, small studies that had suggested women taking the vitamin might have a higher chance of giving birth to twins. This raised alarm because twins often result in premature birth, which can have health complications for the children as well as the mother.

Investigators from the Centers for Disease Control and Prevention in Atlanta and from Peking University assessed that association in the first and largest study of its kind and found no increased risk of twinning from folic acid.

"This is a strong evidence that folic acid is not associated with an increase of twinning," said Robert Berry, principal investigator of the study and a medical epidemiologist in CDC's National Center on Birth Defects and Developmental Disabilities.

"This is good news for women in the United States, in China and around the world," José Cordero, director of CDC's birth defects center, said in a written statement.

In the study, which appears in the Feb. 1 issue of the British journal The Lancet, nearly a quarter of a million Chinese women in their early 20s were taking 400 micrograms of folic acid per day -- the recommended daily amount -- as part of a community campaign to prevent birth defects.

The researchers found a lower rate of twins in women who used folic acid. It made no difference whether the women started using the vitamin before they became pregnant, around the time they became pregnant or afterwards.

" This reassures people there isn't a major downside to taking folic acid before or during pregnancy," Jim Mills, chief of the pediatric epidemiology section at the National Institute of Child Health and Human Development in Bethesda, Md., told United Press International.

Berry said the new findings are more valid than those of the previous studies because those "were small studies and had borderline statistical significance."

In addition, twinning "has been increasing steadily over the past two decades" and this appears to be primarily due to older women having babies and the use of new infertility drugs --both of which increase the likelihood of having twins, Berry said. Both of these factors may have confounded the findings of the earlier studies, he said.

Another explanation is that folic acid may help keep twins viable but not cause them to develop in the first place, Mills said. "It has been known for quite a while now there are a number of pregnancies that have a vanishing twin" in which the pregnancy starts out with twins but ends up with only one child, he said. So the earlier studies may have found an increase in twins among women taking folic acid because the vitamin helped keep both twins healthy until birth.

In this study, the Chinese women stopped taking folic acid after three months. It could be that the vitamin is necessary for longer or throughout the pregnancy to help keep both twins viable, he said.

At this point, both Berry and Mills said folic acid appears safe and women of childbearing age should continue to take it to lower the risk of birth defects if they do become pregnant. Berry noted, "It has to be taken before a woman becomes pregnant. It's too late to start taking it after the woman becomes pregnant."

Government statistics show that over the past 10 years the incidence of spina bifida has declined by 32 percent in the United States and this appears to be largely due to an increase in the number of women who have begun taking folic acid supplements.

Spina bifida -- one of the most common disabling birth defects -- results from the spine not properly closing during the first month of pregnancy. This can result in the spine protruding from the back, paralysis and life-long health problems.

Berry noted the incidence of spina bifida could be reduced further because currently only about 30 percent of women of childbearing age take folic acid supplements.

Steve Mitchell, UPI Medical Correspondent, Washington
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