The role of FISH in prenatal diagnosis of chromosomal anomalies

FLUORESCENT in situ hybridization has multiple applications in prenatal diagnosis. It can be used for the detection of common chromosome aneuploidies of chromosomes 13,18,21, X and Y it can be used for the early detection of segmental imbalances detected in former affected offspring or resulting from balanced translocations in the carrier parents. FISH is also a useful tool for ruling in/out of mosaicism detected in routine chromosomal study as it will provide a means of screening and scoring a larger number of cells than theoretically possible with routine chromosomal study. In this report we are presenting results of prenatal diagnosis cases where we have employed FISH techniques for direct analysis or for confirmation of results otherwise obtained. In a two year period 60 FISH tests have been performed on fetal samples. Forty five cases were tested for 5 common chromosomes ten of these cases were referred for advanced maternal age, 29 for abnormal marker screening test results, and 6 for history of former offspring with chromosome aneuploidy. The remaining cases were tested for other reasons including 4 for microdeletion syndromes previously detected in other offspring, 4 for mosaicism suspected in routine chromosomal study, and 7 for possible imbalance resulting from known chromosome translocation in either parent. In all cases, the results were confirmed with another technique, most often the results of routine chromosomal study and in microdeletion cases, reanalysis on metaphases prepared from cultured cells. There was 100% correlation between the results obtained from the two techniques. Our experience shows that this technique has the advantage of a speedy result with considerable reliability for use in the detection of specific cases. We recommend the application of FISH for all high risk pregnancies.