Objectives: To investigate the effectivity of the first trimester screening (FTS), age and other factors as an indication for invasive testing. Methods: A retrospective analysis of indications for invasive procedures and their effectivity in the group of women who underwent screening in the first trimester of pregnancy in our center. Women were offered the combined screening program by ultrasound and biochemical markers. Women with risk more than 1 : 300 for chromosome 21, 18 or 13 trisomies, or those over the age of 35 as this is still and indication for invasive tests in the Czech Republic were offered genetic counseling and invasive testing. Chorionic villous sampling (CVS) or amniocentesis (AMC) was than performed. Results: Of the 1700 women who underwent FTS, 291 were over 35 in which only 24 had a risk higher than 1 : 300. Detection rate of trisomy 21, 18 and 13 were 100%, (16 cases) for a false positive rate of 4.6%. In the whole screened population 79 had a risk more than 1 : 300. The total number of invasive tests was 150. Amniocentesis was performed in 88 cases, only 27 were done on the basis of screening with 3 aneuploidy detected. 36 amniocenteses were done for age and 25 for other indications - all had normal karyotype. The CVS was performed in 62, 52 on the basis of screening with 13 aneuploidy detected. In the other ten cases 5 for age and 5 for family history the karyotype was normal. Conclusion: Altogether 79 invasive procedures based on screening detected all 16 aneuploidies. Remaining 71 invasive tests (n = 41) for age and (n = 30) for other indications had a complete normal karyotype.

        Key words: first trimester screening, advanced maternal age, indications for invasive procedures, chorionic villous sampling, amniocentesis