[Rapid diagnosis of fetal chromosomal abnormalities by fluorescence in situ hybridization]

In the course of the Down-screening protocol there are possibilities today for rapid diagnosis of aneuploidies among high-risk pregnancies identified by non-invasive screening tests, however, the diagnostic value of these molecular genetic tests are debated.

In this prospective study, data about the reliability of one of the rapid tests, namely; interphase fluorescence in situ hybridization (int-FISH) was to be gathered by the authors.

For the period between May 2002 and September 2006 all of the 1279 fetal sample were examined both with int-FISH and full karyotyping.

Extra or absent signal was detected in 47 cases (3.7%) (trisomy 21 in 32, various other numerical abnormalities in 15 cases). All of these numerical aberrations were confirmed by metaphase analysis without false positivity or negativity. In 19 cases the finding of int-FISH was negative, however, full karyotyping disclosed abnormalities (in 12 of these 19 cases, the abnormality was balanced). Only 4 of the 1279 fetuses (0.3%) (3 small extra marker chromosomes, 1 de novo unbalanced translocation) were to be found, who would have been born with phenotypical abnormalities without metaphase analysis (2 of them had suspect ultrasound signs).

Although more analysis are needed, based on the results of this study it is to be concluded that rapid molecular genetic methods like int-FISH might be accepted as a diagnostic tests of fetal aneuploidy, if its use were restricted to high risk pregnancies identified by advanced maternal age and non-invasive maternal screening only. However, full karyotyping is needed in cases with familial translocation and abnormal 2nd trimester ultrasound signs.