A clinical study on the practicability of trisomy 21 - risk analysis in the first trimester of pregnancy

Background: In the past a non invasive risk analysis for detecting specific chromosomal aberrations was only possible from week 15 of pregnancy. In th is paper the practicability of first trimester screening is analysed. Material and methods: Blood samples were taken from 1000 pregnant women bef ore a invasive prenatal diagnosis was performed. Total hCG, free beta -hCG and PAPP-A (pregnancy associated plasma protein A) was analysed. These data were combined with complete cytogenetic and ultrasonographic (CRL and nuch al translucency- NT) data. Results: In more than 90% of cases the NT was below 3 mm. Here the rate of normal karyotypes was 97.8 %. in 61 cases a abnormal karyotype was found. H ere in the most cases we found an elevated Ni. Also in the most cases of tr isomy 21 and 18 and in triploidies a characteristic ratio of hCG/free beta -hCG and PAPP-A was discovered. Combining NT and biochemical analysis, 85% of trisomies 21 could be discovered as a risk group. Conclusions: This study demonstrates the possibilities of first trimester s creening with a high detection rate for specific chromosomal aberrations. D iscussion: First trimester screening should only be performed in specialise d centers because determination of NT and risk analysis needs extensive exp erience.