The new findings refute a handful of earlier studies linking high folic acid consumption to an increase in miscarriages. In the latest study, women with inadequate folate levels were 50% more likely to have early pregnancy losses, but those with high folate levels did not have a greater miscarriage risk.
The study, published this week in the Journal of the American Medical Association, was conducted by researchers from Sweden's Karolinka Institute in conjunction with the U.S. National Institute of Child Health and Human Services (NICHD).
"This is very encouraging data that suggest we may be reducing the risk of spontaneous abortions in the U.S. by fortifying certain foods," study researcher James L. Mills, MD, an NICHD epidemiologist, tells WebMD.
Folic acid, also known as folate, is a vitamin necessary for proper cell growth and embryo development. Women who get at least 400 micrograms of the vitamin from their diets during the first few weeks of pregnancy can reduce their unborn baby's risk of neural tube defects (NTDs) by as much as 70%. These birth defects include the paralyzing spinal disease spina bifida, and anencephaly, a fatal disease in which the brain does not develop.
Folate deficiency also has been associated with placental separation during pregnancy, pregnancy-induced hypertension, and low blood supply to the placenta. These effects may in part be responsible for the increased risk of miscarriage.
In 1998, the FDA began requiring food manufacturers to fortify certain grain products with folic acid. Many breakfast cereals, rice, pasta, and most breads are now an excellent source of the vitamin, as are beans, leafy green vegetables, and citrus fruits.
Since the FDA move, the number of children born with spina bifida in the United States has decreased by one-third, the CDC announced last month. But Katherine Lyon-Daniel of the CDC's folic acid education campaign tells WebMD that it is still difficult for a woman to know if she is getting enough folic acid through diet alone.
"Almost half of the pregnancies in the U.S. are unplanned, so it is important for all women of childbearing years to get enough folic acid," she says. "One of the easiest ways to do this is to take either a multivitamin or a folic acid or B-vitamin supplement every day if there is any chance at all of becoming pregnant."
The latest study was conducted in Sweden, where the grain supply is not fortified with folic acid. Researchers compared 468 women who had miscarriages between six and 12 weeks of their pregnancies with 921 women who were also in their first trimester, but had not miscarried.
Women with folate deficiencies were 50% more likely to experience early pregnancy losses. Women who had high levels of folate in their blood were no more likely to have miscarriages than those who had lower levels.
In the group of women with low folate levels a miscarriage was significantly more likely to occur if the fetus had an abnormal chromosome.
The researchers concluded that countries that have fortified their food supplies with folic acid and those considering it can trust that fortification most likely will not increase spontaneous abortion rates and might even decrease them.
"Our study did not show any increase in spontaneous abortions at all, in fact it went in the opposite direction," Mills says. "That is extremely reassuring."