RPMG will now be using comparative genomic hybridization (CGH) for preimplantation genetic screening (PGS) for chromosome screening of embryos (including for sex selection). CGH is a technique that involves amplifying the DNA and uses many thousands of probes to check all 23 chromosome pairs. As long as an intact nucleus is biopsied, it is virtually error-free, whereas with the older technique, fluorescence in-situ hybridization (FISH), many errors may occur because FISH relies on binding of a single probe to each chromosome, and there are potential cell fixation artifacts, overlapping signals, and a subjective microscopic analysis is required. It also does not analyze all chromosomes. Unfortunately many normal embryos have been discarded with that technique due to these artifacts, and false negative results have also occurred where an embryo appeared normal but was actually abnormal.