Advanced FISH with directly labeled X, Y and 18 DNA probes as a tool for rapid prenatal diagnosis.

OBJECTIVE: To examine a rapid technique for identification and determination of fetal sex chromosomes and one autosome (chromosome 18) in uncultured amniotic fluids using fluorescence in situ hybridization (FISH) with directly labeled DNA probes and ignoring the use of proteinase K and Rnase. STUDY DESIGN: Twenty-five amniotic samples taken from pregnant women who were in their 18th gestational week and had advanced maternal age were studied for analysis of sex chromosomes and chromosome 18 with the FISH technique as well as standard cytogenetic analysis. RESULTS: Four hours after amniocentesis was performed, we identified the sex of the fetuses and disomy of chromosome 18 in a minimal sample of uncultured amniotic fluid by using directly labeled DNA probes for chromosomes X, Y and 18 (VYSIS) and ignoring the use of proteinase K and Rnase. CONCLUSION: The possibility of shortening the time required for identification of aneuploidies in a second-trimester fetus is useful in cases where fetal anomalies are ultrasonically diagnosed at a relatively advanced gestational age.