Embryos can be genetically tested before transfer back to the mother. Tests currently used require viable cell DNA, which can be obtained from an embryo starting from Day 3. The cells inside an embryo are called blastomeres, and there are about eight blastomeres in a Day 3 embryo. Each of the eight blastomeres has the potential and genetic material to form a complete human being. As seen in identical twins transferring each of the eight blastomeres to a separate person can result in 8 babies. Thus one or two blastomeres from a Day 3 embryo can be taken out for genetic testing, and this procedure is called Embryo Biopsy.
Genetic testing can be performed at an early stage embryo by removing and testing the Polar Body. The embryo at its later stages are called Blastocysts, and Blastocyst Biopsy can be performed to remove a cluster of cells for genetic testing. Cells are removed after the biopsies are tested using the FISH and PCR techniques.