ATLANTA — The Centers for Disease Control and Prevention estimates mandatory fortification of enriched cereal grains with folic acid prevents more than 1,300 cases of neural tube defects annually in the United States.

Neural tube defects are birth defects of the brain and spine that occur early in pregnancy as a result of improper closure of the embryonic neural tube. The Food and Drug Administration mandated folic acid fortification of enriched cereal grain products in 1998.

A new study appearing in the Jan. 16 issue of the C.D.C.’s “Morbidity and Mortality Weekly Report” examined data from 19 population-based birth defects surveillance programs in the United States covering the years 1999-2011. The number of births occurring annually without neural tube defects that otherwise would have been affected was about 1,326, according to the C.D.C., Atlanta. The C.D.C estimated preventing that many cases leads to annual savings of $508 million in total direct costs.

“Mandatory folic acid fortification remains an effective public health intervention,” the C.D.C. said.

Using data from all the programs, the C.D.C. found a 28% reduction in the prevalence for anencephaly and spina bifida, the two most common neural tube defects. The percentages were 35% for programs that systematically conducted prenatal ascertainment to capture diagnosed cases and 21% for programs that did not.

Fewer Hispanic women (17%) than non-Hispanic white women (30%) reported consuming 400 micrograms or more of folic acid per day through fortified food or supplements. Taking this evidence into account, the C.D.C. said fortifying masa corn flour with folic acid at the same level as enriched cereal grain products likely would prevent an additional 40 cases of neural tube defects annually.