A pragmatic, multicentre, randomized double-blind controlled trial with an intention-to-treat analysis, of the use of preimplantation genetic screening (PGS) for aneuploidy by means of microarray comparative genomic hybridization (CGH) for the chromosomal analysis of the polar bodies (PB) of oocytes collected after ovarian stimulation for in vitro fertilization (IVF), and with the intention to assess the genetic competence of oocytes of advanced biological age, and the effect of this technique on reproductive outcome.