Congenital heart disease. what are the chances that somebody makes it to adulthood without ever getting diagnosed?

Good: Less serious congenital heart defects are often not diagnosed till later in childhood or even during adulthood.These are usually not immediately life threatening.The more serious congenital heart defects are usually evident soon after birth! and usually diagnosed during pregnancy.

Depends: It depends on the type of congenital malformation. There are some serious congenital heart defects that can be diagnosed in utero and some obvious upon birth. Others, like anomalous origin of the coronary artery or a patent foramen ovale may never cause any trouble and may not ever be recognized unless an evaluation or test for other reasons happens to demonstrate the anomoly.

Less Than Before: With most women having ultrasound testing, and better technology, the majority of serious defects are now diagnosed prenatally. There still are many that may be diagnosed as they develop, such as hypertrophic subaortic stenosis, which shows up as you age.