OBJECTIVE To investigate changes over time in the prevalence at live birth of cardiovascular malformations and to compare “anatomical” and “physiological” diagnostic hierarchies within a population.

DESIGN Retrospective and prospective ascertainment of all congenital cardiovascular malformations diagnosed in infancy.

SETTING The resident population of one health region.

PATIENTS All infants live born from 1985 to 1997 with cardiovascular malformations confirmed by echocardiography, cardiac catheterisation, surgery or autopsy.

MAIN OUTCOME MEASURES Year to year variation in prevalence of individual malformations and of “complex”, “significant”, and “minor” groups.

RESULTS 2671 babies with cardiovascular malformations were confirmed in a denominator population of 477 960 live births (5.6 per 1000). There was no change over 13 years in the birth prevalence of “complex” or “significant” defects, but a highly significant increase in “minor” defects (p < 0.0001), mainly small ventricular septal defects. Termination of pregnancy increased from no cases in 1985 to 16 in 1997 with no demonstrable effect on live born babies with heart defects. A one dimensional “anatomical” diagnostic hierarchy led to under ascertainment of pulmonary atresia by 27%, coarctation of the aorta by 39%, and interruption of the aorta by 100%.

CONCLUSIONS The apparent increase in live born cardiovascular malformations results mainly from improved diagnosis of minor defects. There has been no change over time in birth prevalence of more serious defects. Spontaneous year to year variation in numbers will make it difficult to ascribe any short term changes to any particular intervention. A two dimensional diagnostic hierarchy is offered as a standard.