In 1992, the U.S. Public Health Service recommended that all women of child-bearing age take 400 micrograms of folic acid each day as a way to help prevent certain types of birth defects. In 1998, the United States required makers of most grain products to add 140 micrograms of folic acid. Now, the Centers for Disease Control and Prevention reports these steps prevent about 1,300 neural tube birth defects each year.
Neural tube birth defects are major birth defects of the brain and spine. They occur very early in pregnancy when the neural tube of the embryo does not close properly. The two most common neural tube defects are spina bifida, where the lower spine has not formed correctly, or anencephaly, where the head or brain has not formed correctly.
The CDC issued two reports, one on the prevalence of neural tube defects from 1995 to 2011, after mandatory folic acid fortification, and a second paper on the use of dietary supplements and other characteristics among women who had one pregnancy affected by a neural tube defect. The second paper found that women who had had a baby with a neural tube defect who took high doses of folic acid-4 milligrams per day-with a subsequent pregnancy were less likely to have a baby with a defect than those who did not take folic acid.
Women are urged to take a high-dose folic acid supplement starting at least 4 weeks before becoming pregnant and at least through the first three months of the pregnancy.
The report also notes that Hispanic women are about 20% more likely to have a child with a neural tube defect than non-Hispanic white women. One reason may be that although wheat flour is fortified with folic acid, the corn flour that is more popular with Hispanic families is not.
Since the rule requiring grain foods to be fortified with folic acid, the number of babies born with neural tube defects has declined by 35%, according to the March of Dimes, an organization that works against birth defects and for healthy pregnancies and babies.