Trisomy 21 is one of the most common chromosomal abnormalities in live born children and causes Down syndrome. Molecular analysis has revealed that the 21q22.1-q22.3 region appears to contain the gene(s) responsible for the congenital heart disease observed in Down syndrome. Trisomy 13, also called Patau syndrome, is a chromosomal condition that is associated with severe mental retardation and certain physical abnormalities. The critical region has been reported to include 13q14-13q32 with variable expression, gene interactions,or interchromosomal effects. The RCAN1 (21q22) specific FISH probe is optimized to detect copy numbers of chromosome 21 at 21q22 on uncultured amniotic cells. The RB1 (13q14) specific FISH probe is optimized to detect copy numbers of chromosome 13 at 13q14 on uncultured amniotic cells.