incidence of birth defects in USA

question: What is the incidence of birth defects today in the United States?

The risk for major malformations among the general population today is around two percent. Certain segments of the population, however, such as women with insulin-dependent diabetes and those who have given birth previously to a child with neural tube defects, have an increased risk of delivering malformed babies compared to the general population. In both of these latter instances, metabolic or nutritional factors are certainly important.
source :An Interview with James L. Mills, M.D.,ificinfo.health.org