The majority of abnormal embryos are indistinguishable from normal embryos when studied using a microscope. Therefore, normal embryo appearance cannot be used to evaluate for chromosome abnormalities. It is said that even if the eggs and sperms are taken from normal healthy young couples, almost 40% of embryos will be genetically abnormal. If the woman is older, has bad quality eggs or if the man has poor sperm quality, 60-90% of the embryos may be abnormal.
It is very important to identify embryos with the correct number of chromosomes for successful IVF outcome.
Pre-implantation genetic screening (PGS) is used in conjunction with in-vitro fertilization (IVF) to screen embryos for any abnormalities in the number of chromosomes (ploidy). The information obtained from PGS helps IVF physicians and patients decide which embryos to transfer.
Extra or missing chromosomes is called aneuploidy. Aneuploidy is responsible for the vast majority of spontaneous miscarriages and can result in birth defects and mental retardation in live born babies. A common example is an extra copy of chromosome 21 (Down syndrome or trisomy 21).
|Common Aneuploidies in autosomes||Common Aneuploidies in Sex chromosomes|