A number of studies have now confirmed that a high proportion of oocytes and embryos derived from IVF procedures have genetic abonormalities. A oocyte or embryo with no abnormality is termed euploid, and oocytes or embryos with abnormalities are termed aneuploid. Aneuploidy in oocytes and embryos leads to poor IVF reproductive outcomes, such as, a lower implantation chance (pregnancy chance) and a higher chance for pregnancy loss. In IVF the selection of embryos or blastocysts for cryopreservation or the transfer to a patient uterus is still mostly based on morphological characteristics. However, morphology alone has been shown not to be able to exclude aneuploid embryos or blastocysts totally. Screening embryos or blastocysts before use has been shown to improve the chances of implantation and reduce the chances of pregnancy loss. In the past the only technology available was fluorescence in situ hybridization (FISH), which had limited success because it was only able to screen a limited number (5-12) of chromosomes. The new technology available such as comparative genomic hybridization (CGH) have the advantages of being able to screen all 24 chrosomes, thereby producing a more reliable and accurate result. Although abnormalities persist to the blastocyst stage there is evidence to suggest that a larger proportion of blastocysts are euploid (genetically normal) than cleavage stage embryos. The use of blastocysts therefore have an advantage over the use of cleavage stage embryos, because of the lower incidence of abnormalities and more than one cell can usually be screened (increasing overall accuracy). The pregnancies achieved at Antalya IVF using aneuploid screened blastocysts show the pregnancy chance when replacing one screened blastocyst may be as much as 20% higher than when replacing 2 fresh unscreened blastocysts.