After fertilization, biopsy was obtained from cleavage stage embryos. FISH analysis was used to distinguish embryos with balanced and unbalanced chromosomal abnormalities for carriers of structural chromosomal aberrations. In the analysis of translocations, unique FISH probes that flank the breakpoints of each translocation or that require the use of subtelomeric probes (specific to the chromosome ends of the translocated segments) for each affected individual must be designed and validated to detect normal and balanced products in embryonic tissue.