FISH (fluorescence in situ hybridization), aCGH (array comparative genome hybridization) and NGS (Next Generation Sequencing) are the three main platforms available for preimplantation genetic screening.
FISH is the oldest technology used in PGS. FISH applies fluorescent labels to a specific region on 12 or fewer chromosomes. The embryos are fixed on a microscope slide, labeled, and observed under fluorescence microscopy for copy chromosome evaluation. Because FISH looks only at one specific location of the chromosome, large deletions and insertions are unlikely to be detected. Because it examines only a small fraction of chromosomes (usually five) it misses many potential problems.
Array CGH (aCGH) is similar to FISH in that it uses fluorescence detection, but it does so at a larger scale, ranging from thousands of probes (aCGH) to hundreds of thousands of probes (SNIP array). Array CGH is the most common platform used in PGS and is substantially better than FISH. However, it is known to have several limitations resulting in an approximately 3% false positive and false negative rate.
NGS (Next Generation Sequencing) is the latest technology used in PGS. NGS reads the actual DNA sequence on each chromosome to directly determine the presence or absence of chromosomes, and can reach very high resolution allowing the detection of single mutations. Because NGS does not rely on fluorescence, the chance of false negative or false positive results is substantially reduced.