in the Czech Republic in 1996-2004. Type of study: A retrospective demographical – epidemiological analysis of data from a National Register of Congenital Anomalies of the Czech Republic. Methodology: Data on birth defects in the Czech Republic from the Institute of Health Information and Statistics - National Register of Congenital Anomalies from the 1996 – 2004 period and a control group data on healthy children born to mothers taking medications from the same time period. Data on medication were analyzed in relation to particular defects and were also used in international databases. Results: There were 1,125 children born with a birth defect to mothers taking 1st trimester medication making a total of 1,456 particular birth defects. A control group covered 1,321 exposed women giving birth to a child without any birth defect. Some types of congenital heart defects, cleft lip with cleft palate and limb reduction defects. A significantly higher risk was found also in following 5 types of drugs: anticoagulants, antihypertensives, peripheral vasodilatants, urologics and antiepileptics. Conclusions: A significantly higher risk was found for the following defects: anencephaly, spina bifida, congenital hydrocephalus, anophthalmia/microphthalmia and auricular and limb reduction defects. Although the results are not always unambiguous and are probably influenced by both information and recall bias, they complement data on adverse effects of drugs in pregnancy in the Czech Republic. They also stress the need for a high preliminary caution in drug prescription and for a complex and individual risk assessement by a clinical geneticist.

        Key words: birth defect, populational teratology, teratogen, incidence, Czech Republic