Objective: Presentation of the incidence of congenital hydrocephalus in the Czech Republic during 1961 to 2000, prenatally and postnatally diagnosed cases with this defect. Analysis of the prevalence of the defect in different groups by maternal age. Design: Retrospective demographic epidemiological study. Setting: Institute for the Care of Mother and Child, Prague. Method: In the investigation data from the nationwide registration of birth defects were used, kept in in the Institute for Health Information and Statistics of the Czech Republic and data on the prenatal diagnosis from different departments of medical genetics. Epidemiological analysis of the incidence of congenital hydrocephalus diagnosed prenatally and postnatally in the Czech Republic in 1961 to 2000. Mathematical and statistical analysis of the prevalence of this defect by maternal age, the method of calculation of the 95% confidence interval was used. Results: In the Czech Republic in 1961–2000 3650 cases of congenital hydrocephalus were recorded. From this total number of notified cases 3415 cases were diagnosed after delivery. Prenatally 235 cases were diagnosed and pregnancy was terminated prematurely. The mean incidence of birth hydrocephalus in the neonatal population in the CR in 1961–2000 was 6.11 per 10 000 liveborn infants, after adding the number of prenatally diagnosed cases the mean incidence was 6.35 per 10 000 liveborn infants. The mean success rate of prenatal diagnosis during the investigation period was 24.30%. Conclusion: The authors found a significant decrease of the incidence in the neonatal population of the Czech Republic due to advances in prenatal diagnosis during the last nine years. When evaluating maternal age as one of the risk factors for the development of congenital hydrocephalus a statistically significantly higher risk was recorded in women above 37 years of age.

        Key words: birth defect, congenital hydrocephalus, incidence, Czech Republic, prenatal diagnosis, maternal age