Objective: Analysis of incidence of birth defects in general and the proportion of individual types of birth defects within the framework of registration of inborn defects in the period of 1961-2000 in the Czech Republic. Design: A retrospective analysis based on registered birth defects from the material of Institute of Care for Mother and Child and IHIS from the period of 1961-2000. Methods: The authors compared the real frequency of birth defects in the eighties and nineties with expected frequency calculated on the basis of mean values from the sixties and seventies. Results and conclusions: The results between the expected and estimated values of the overall frequency of birth defects are based on two reasons. First of all there are changes in registration as such – increased numbers of registered types of birth defects, prolonged period of reporting the inborn defects up to 15 years old children, decreased levels of foetus viability and other factors. There is also the change of frequency caused by all-population changes (eradication of some infections, vaccination rate in the population, improved nutrition of the population, year-around availability of vitamins), the development of diagnostic methods (ultrasonographic methods) and, especially, the role of prenatal screening and prenatal diagnostic methods in practice.

        Key words: birth defect, prenatal diagnostics, epidemiology