Congenital heart defect is the commonest form of major birth defects, affecting 6-8/1000 live births. There are different types of malformations, and not all of them cause the baby to appear blue.
The term "cyanosis" is used to describe the blue discolouration of the skin caused by insufficient oxygen in the blood. Those causing cyanosis may be evident at birth. Those without cyanosis – the acyanotic group – may only be detected weeks, months or even years later.
Some forms of CHD only cause cyanosis in later life when the condition deteriorates. Most (up to 60%) of babies with CHD are diagnosed by one month of age, and many of them remain inoperable. However, during infancy and childhood further development normally occurs in the child’s cardiovascular system. Changes in the operating pressures of the right and left ventricles may then bring to light a previously unknown mild form of CHD, so that the diagnosis is made much later.
CHD in adults is a combination of congenital and acquired problems. A congenitally deformed valve will cause the blood flowing over it to be turbulent. This produces gradual stiffening and hardening of the valve, so that what was an insignificant abnormality in a child, in the adult becomes a problem needing surgery.
(The Heart and Stroke Foundation/Health24, updated January 2008)