Rapid detection of chromosome aneuploidies in fetal blood and chorionic villi by fluorescence in situ hybridisation.

OBJECTIVE

Evaluation of fluorescence in situ hybridisation in the detection of numerical aberrations involving chromosomes X, Y, 13, 18 and 21.

SETTING

Harris Birthright Research Centre for Fetal Medicine.

SUBJECTS 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 chromosomal abnormality. Karyotyping was performed by both traditional cytogenetics and fluorescence in situ hybridisation, using commercially available kits which utilise a heterochromatic Y probe and the alpha satellite repeat probes for chromosomes X, 18, and 13/21. The frequency distributions of the number of signals obtained by fluorescence in situ hybridisation in the chromosomally normal and abnormal fetuses were compared.

RESULTS

Traditional cytogenetic analysis demonstrated that the 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, Turner's or triploidy within six hours of sampling; 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

In detection of fetal numerical chromosomal abnormalities the use of the combined 13/21 probe cannot provide sufficiently accurate results to justify abandonment of traditional cytogenetics in favour of fluorescence in situ hybridisation.