Why hasn't the age adjusted incidence of chd has not declined in the last 40 years?

?congenital heart ?: The frequency of congenital heart defects is dependent on the interplay of genes on a variety of chromosomes along with environmental factors. Over time, our diagnostic & therapeutic capabilities have improved, but that might increase, not decrease the gene frequency & incidence over multiple generations.Survivors of once fatal chd now grow up & add to the gene pool.Diverse toxic exposures continue.