Study Finds No Link Between Taking Folic Acid and Having Twins

New results from a study involving almost a quarter of a million women in China show that taking folic acid to reduce the risk of neural tube birth defects does not increase a woman's chances of giving birth to twins.

Multiple studies conducted during the past several decades have shown the consumption of folic acid before conception and during pregnancy can reduce the incidence of spina bifida and other neural tube defects. However, the results of some earlier, smaller studies raised the question of whether an increase in multiple births can be associated with the consumption of vitamin supplements containing folic acid during pregnancy.

This is the first scientific study of its kind done on a large population of young women with accurate records of their folic acid use before conception and during the early months of pregnancy. These women used folic acid without other vitamins.

Twin pregnancies often result in premature birth, leading to complications and long-term health problems for the children. But this new study finds no evidence of a link between folic acid consumption and multiple births.

“This is good news for women in the United States, in China, and around the world,” said Dr. José Cordero, the director of the CDC's National Center on Birth Defects and Developmental Disabilities. “Taking folic acid before and during early pregnancy to prevent some serious birth defects in their babies should not increase a woman’s chances of having a twin pregnancy.”

Among the 242,015 women in the study, there was no difference in the rates of twin births for women who took a daily pill containing 400 micrograms of folic acid before conception and during early pregnancy, compared with those who did not take any folic acid (less than 1 percent in each group). This particular study focuses on women who had participated in a previous project to prevent neural tube birth defects by taking 400 micrograms of folic acid a day in pill form.

Over the past decade in the United States, the incidence of spina bifida has been reduced by 32 percent. This decrease followed the Public Health Service’s 1992 recommendations urging women to increase their levels of folic acid prior to becoming pregnant.

The study, which appears in the February 1 issue of Lancet, was conducted by the CDC and the Peking University Health Sciences Center in China. The project, conducted in China, was a collaborative effort between lead author Zhu Li, M.D., M.P.H., and other researchers from the Peking University Health Sciences Center, China with R.J. Berry, M.D., M.P.H.T.M. and other researchers from the CDC’s National Center on Birth Defects and Developmental Disabilities.

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