is a form of genetic testing that you can elect to have performed on your embryos. CGH tests all all 23 pairs of chromosomes. PGD is another form of embryonic genetic testing, however, it only examines some of the 23 pairs. If you want more info, there is a long thread further down, dating back 2 or 3 weeks.
We decided to test in order to optimize our chances. Also, we are only tranferring one embryo, because we don't have the bandwidth for twins (or more), so we really want to maximize our chances.