Measurement of disease occurrence is usually expressed as the incidence, defined as new cases in the at risk population in a specific time period.

  • Some cardiovascular malformations are determined at the moment of fertilization while others originate at later stages of intrauterine life initiated by infection or toxic exposure. There may be throughout pregnancy : ongoing causation (incidence) , loss of severely affected embryos (mortality) and possibly the removal of cases by healing. True incidence would include cases with lethal anomalies never seen in liveborns.
  • The term prevalence-at-live-birth refers to the cases found in the population at a specific point of time.

It is obvious that the kinds of cases recognized in the early decades of Pediatric Cardiology would be different from those recognized and treated after the following developments:

  • the introduction of cardiac surgery in the 1950s
  • the development of open heart surgery in the 1960s
  • the improvement of infant transport systems in the 1970s
  • the non-invasive ultrasound diagnostic methods for detecting defects in the 1980s.

This last diagnostic change occurred during the BWIS study period and resulted in a dramatic increase in cases of small ventricular septal defect and of cases of mild pulmonic stenosis (Wilson, 1993, Martin, 1989).The dramatic differences resulting from changes in diagnostic methodology were illustrated also in the detailed evaluation by of the EUROCAT subproject on congenital heart disease (Pexieder and Bloch, 1995) . A comparison to the BWIS data, gathered in the same time period, and using a similarly defined subset of diagnoses, revealed differences, which could be explained by knowledge of the different practices on the two continents.

Selected References