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Excess folic acid boosts chances of twins after fertility treatment

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Increasing folic acid intake increases the chances of twins for women undergoing in vitro fertility treatments in which more than one embryo is transferred, a new British study suggests.

However, folic acid, a B vitamin that protects against birth defects such as spina bifida, does not affect overall chances of becoming pregnant after fertility treatment, the researcher says.

"Our experience is that women undergoing IVF (in vitro fertilization) are very health-conscious, and they may be taking multivitamins and folic acid -- not realizing that the multivitamin contains folic acid," says the study's lead author, Paul Haggarty, of the University of Aberdeen. "We would recommend to women undergoing IVF not to exceed the recommendations."

But women who are pregnant or seeking to become pregnant shouldn't reduce their consumption of the vitamin, experts advise.

"This should not discourage the general population from taking folic supplementation. This study does not apply to the general population of women getting pregnant," says Dr. Jennifer Wu, an obstetrician and gynecologist with Lenox Hill Hospital in New York City. "Folate has been proven to decrease the number of neural tube defects, and spina bifida can be a lifelong, devastating condition."

Spina bifida is a neural tube defect, involving incomplete development of the brain, spinal cord, and/or their protective coverings, caused by the failure of the fetus' spine to close properly during the first month of pregnancy, according to the U.S.

National Institutes of Health.

The United States started fortifying flour with folic acid in 1998, a move that corresponded with an 11 percent to 13 percent increase in the incidence of multiple births after fertility treatments. Since U.S. health officials began recommending consumption of folic acid before pregnancy in 1992, the rate of spina bifida has dropped 32 percent, according to the U.S. Centers for Disease Control and Prevention.

The British government is now considering a similar initiative, as about 900 babies are born with spina bifida each year in that country.

"We are basically very supportive of this because 50 percent of women are not planning to become pregnant when they become pregnant, so it doesn't matter how good your advice is. They're not going to take it up," Haggarty says. "The only way around that is to improve overall folic status if you want to reduce the incidence of spina bifida."

The question, though, is how this initiative might affect multiple births.

The norm in IVF treatment is to transfer more than one embryo to the womb, thus increasing the chances of a live birth. This, of course, results in a higher likelihood of having twins.

"The known inherent risk of IVF anyway is multiple gestation," Wu says. "It's also a cost issue. Each cycle of IVF is so expensive that many couples will take their chances of having twins over nothing at all."

For this study, Haggarty and his colleagues looked at folate (folic acid) intake, blood concentration of folate and variations in five genes related to folate metabolism in 602 women undergoing IVF treatment. The study findings appear in the May 6 issue of the journal The Lancet.

Women with higher blood concentrations of folate who had two embryos transferred had a higher rate of twin births. Folate levels did not affect their chances of getting pregnant, however.

The researchers also found a link between one of the genes involved in folate metabolism and the success of IVF treatment.

"A gene which is involved in the metabolism of folate was predictive of whether the treatment would be a success, and it was also predictive of the woman's history of infertility," Haggarty explains.

The message for women undergoing IVF treatment and for their health care providers is to regulate folic acid intake, Haggarty says.

"There is an intersection between the two groups trying to do the best for people, one is for spina bifida and the other is IVF practitioners. We have to be careful of that," he says. "The way around that is probably for IVF practitioners to try to transfer one embryo when they can, and for women to not go too high with their folate intake."

(The HealthDay Web site is at

c.2006 HealthDay News

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