Birth defects encompass structural or functional abnormalities present at birth that lead to physical or mental disability, and in severe cases, fatality. Thousands of variations of these defects have been identified by researchers. Presently, birth defects stand as the primary cause of infant mortality within the first year of life, according to the March of Dimes Birth Defects Foundation. They define birth defects as anomalies in structure, function, or metabolism (body chemistry) present at birth, resulting in physical or mental disability, or in fatal outcomes.