Analysis of amniotic fluid specimens for common chromosome disorders using interphase fluorescence in situ hybridization.

OBJECTIVE The aim of the study was to examine the usage of multi colour FISH technology as an adjunct to conventional cytogenetics for the prenatal diagnosis of aneuploidy in interphase nuclei from high risk pregnancies. METHODS Amniotic fluid samples were collected for interphase FISH analysis using DNA probes for chromosomes 13, 18, 21, X and Y. All the probes were directly labeled with fluorescent molecules. Fluorescent signals were observed under a microscope. A minimum of 100 nuclei with defined hybridization signals were counted for each probe. RESULTS Seventy-eight amniotic fluid samples were received for FISH analysis. The average age of mothers and their gestational ages were 33 years and 17.5 weeks respectively. Triple test screening was positive in 39.5% of the women followed by advanced maternal age and ultrasonographic abnormalities. Interphase FISH was performed on 76 specimens whereas 2 samples were rejected because of blood contamination. Aneuploidy was identified in 6 out of 76 specimens. Two cases of trisomy 21, two cases of trisomy 18 and one case of monosomy X were detected. In addition, one case showed 10% mosaicism for trisomy 21. Initially 4 (5.3%) samples were uninformative due to technical reasons but gave acceptable scoring signals when reanalyzed. CONCLUSION This study has demonstrated that interphase FISH is a rapid and a reliable technique for the enumeration of chromosome number in uncultured amniocytes. Clinicians can use it for making early decisions necessary for the management of high risk pregnancies ultimately saving patients from anxiety and psychological stress.