Aim and type of study: A retrospective study and analysis of data on gestational week at the time of the birth defect diagnoses of both invasive and non-invasive type as well as on gestational week at the time of pregnancy termination in the Czech Republic over the 1996 – 2003 period. Methodology: Data on prenatal diagnostics were obtained from particular departments of medical genetics. Data were collected for both birth defects as a total as well as for selected particular types: anencephaly, spina bifida, omfalocele, gastroschisis and Down syndrome. An analysis on gestational weeks at the time of diagnosis and/or pregnancy termination was performed. Results: Mean gestational week at the time of diagnosis was 19.49 for total birth defects and 20.02 for pregnancy termination. Corresponding values (diagnosis x termination) in gestational weeks were as follows: Anencephaly 17.01 and 17.69, spina bifida 19.41 and 19.68, omfalocele 17.64 and 17.99, gastroschisis 17.63 and 18.36, Down syndrome 19.81 and 20.43 Conclusions: Results of aggregate data analysis contribute to a better knowledge of different methods of prenatal diagnosis during different gestational periods. All values of mean gestational week at the time of diagnosis/pregnancy termination slightly decreased during the time of the study in all presented types of birth defects. This study was supported by an IGA MZ CR grant NJ 7516-3.

        Key words: birth defect, anencephaly, spina bifida, omfalocele, gastroschisis, Down syndrome, gestational week