BACKGROUND: Single-embryo transfer is a well-accepted strategy to avoid multiple pregnancies in an assisted reproductive technology programme. The selection of the embryo with the highest implantation potential is a crucial step. Besides the morphological quality and embryo kinetics up to the blastocyst stage, pre-implantation genetic screening (PGS) of aneuploidy has been advocated as an adjuvant approach by which to select the right embryo for transfer.