Aging of human eggs starts after 30 years old. It results in the increase of amount of eggs with spontaneously occurred mistakes in the chromosome number.
The percentage of abnormal eggs and embryos grows with the age of a woman. If we look into the pool of eggs collected in one egg collection there will be around 20-25% of abnormal eggs in the age of 30, 40-45% of abnormal eggs in the age of 35 and 70-75% of abnormal eggs in the age of 40. The percentage of abnormal eggs grows dramatically after the age of 40 so that it is hardly possible to find normal eggs in the age above 43 [D. Wells, 2013]. As a result 1 in 4 morphologically good blastocysts is aneuploid in the age of 30, and 3 in 4 morphologically good blastocysts are aneuploid in the age of 41. [Ata, Munne al 2012 – 875 cycles, 4600 embryos]
Conclusion: The percentage of abnormal embryos increases with the age of an egg.
Hence a reliable method is required to sort aneuploid embryos out before embryo transfer. This method is called PGS – pre-implantation genetic screening. Contemporary PGS techniques allow testing for all 46 chromes.