Objective: Evaluation of the efficiency of detection of inborn chromosomal aberrations by bioche- mical screening of pregnant women. Design: Summary of 9-years study by karyotyping of amniocytes of pregnant women, when patho- logical levels of AFP, hCG, uE3 were detected. Ethical problems of genetic counselling of pregnant women. Setting: Department of Medical Genetics FTN, Chair of Medical Genetics IPVZ, Prague 4. Methods: Biochemical screening of pregnant women in II. trimester of pregnancy by Triple Test and computer programme Prenatal Software 1.2.K, cytogenetical examination of amniocytes from amniotic fluid after amniocentesis in II. strimester. Results: Among 6 471 pregnant women tested by Triple Test 20 % had abnormal levels of test. In 1.5% of them an abnormal fetal karyotype was detected. Only 1/3 of them were Down Syndromes, we found also other types of aberrations. During ethicaly suitable counselling only 2/3 of pregnant women decided to terminate the pregnancy. Conclusion: Biochemical screening of pregnant women in II. trimester is very important help for detection of inborn chromosomal aberrations. The women must be informed by suitable ethical approach.

        Key words: biochemical screening in pregnancy, Triple Test, amniocentesis, chromosomal aberra- tions