Role of Aneuploidy on Embryo Implantation

Approximately 30% of oocytes in the human species carry a chromosomal imbalance. This condition has severe clinical consequences as approximately one-third of spontaneous abortions are aneuploid. The most obvious link to the increase of aneuploidy in oocytes is maternal age. This has been directly confirmed by the analysis of polar bodies. Their analysis permits to give confirmation of the high predisposition of oocytes to meiotic errors. Also, the study of chromosomes on sperm has revealed a frequency of 6-7% aneuploidy in normal sperm samples, and is significantly increased in cases of severe oligoasthenoteratospermia or azoospermia due to testicular failure. During the preimplantation period there is a progressive loss of abnormal embryos at specific stages in early development, through growth arrest and degeneration of abnormal embryos. The frequency of chromosomal abnormalities is strictly related to the category of patients (advanced maternal age, repeated cycles, altered karyotype, repeated miscarriages, TESE). Based on these considerations, preimplantation genetic diagnosis for aneuploidy is proposed in reproductive medicine with the finality of improving the clinical outcome after IVF. Substantial evidence has been accumulated on the positive impact of the technique, reporting increased implantation rates and a concomitant decrease of spontaneous abortions and trisomic pregnancies.