RAPID DETECTION OF CHROMOSOME ANEUPLOIDIES IN FETAL BLOOD AND CHORIONIC VILLI BY FLUORESCENCE IN-SITU HYBRIDIZATION

Objective Evaluation of fluorescence in situ hybridisation in the dete ction of numerical aberrations involving chromosomes X, Y, 13, 18 and 21. Setting Harris Birthright Research Centre for Fetal Medicine. Subj ects and methods Chorionic villi (n = 45) or fetal blood (n = 34) were obtained from 79 pregnancies undergoing fetal karyotyping at 10 to 39 weeks of gestation because of ultrasonographic markers of fetal chrom osomal abnormality. Karyotyping was performed by both traditional cyto genetics and fluorescence in situ hybridisation, using commercially av ailable kits which utilise a heterochromatic Y probe and the alpha sat ellite repeat probes for chromosomes X, 18, and 13/21. The frequency d istributions of the number of signals obtained by fluorescence in situ hybridisation in the chromosomally normal and abnormal fetuses were c ompared. Results Traditional cytogenetic analysis demonstrated that th e fetal karyotype was normal in 47 cases and abnormal in 32 (including 24 with trisomies 21, 18 or 13, three with triploidy, one with Turner s syndrome and four with translocations, deletions or mosaicism). With fluorescence in situ hybridisation it was possible to obtain accurate diagnosis of trisomy 18, Turners or triploidy within six hours of sam pling; signal distributions with these chromosomal abnormalities were very different from those of normals. However, for trisomies 21 and 13 there was an overlap in values with those from normals. Conclusions I n detection of fetal numerical chromosomal abnormalities the use of th e combined 13/21 probe cannot provide sufficiently accurate results to justify abandonment of traditional cytogenetics in favour of fluoresc ence in situ hybridisation.