The Different Biopsy Techniques

Abstract

Preimplantation genetic testing needs access to genomic DNA in order to execute a genetic test on a preimplantation embryo. Normally a few cells must be extracted or ‘biopsied’ from the embryo to achieve this. Embryo biopsy evolved from attempts in the 1960s and early 1970s to sex farm animal embryos to now utilizing it to screen and select human embryos based on Ploidy, or avoid monogenic disorders. In October 1989, the first clinical cleavage stage biopsies and single cell PGT to determine the sex of the embryos were conducted. It has now evolved to utilize Trophectoderm cells. The advent of Laser has allowed the biopsy process to shift away from mechanical and chemical hatching and techniques also now involve Laser to separate the cells from the blastocyst. Here is a short summary of the different biopsy stages. Polar Body Biopsy : — Polar bodies are small cells produced during the process of oogenesis (egg development) in females. — Since polar bodies contain genetic material from the egg, they can be biopsied to indirectly infer the genetic status of the egg. — This technique is less common and has limitations, but it can be used in certain situations. Blastomere Biopsy (Day 3 Biopsy) : — Performed on the third day after fertilization when the embryo has around 8 cells. — A single cell (blastomere) is removed from the embryo for genetic testing. — Mosaicism cannot be ruled out thus questioning the efficacy of this technique. Trophectoderm Biopsy (Day 5-7 Biopsy) : — Performed at the blastocyst stage, typically on the fifth or sixth day of embryonic development. — Usually, 5-10 cells from the trophectoderm are removed for genetic testing. — This technique is now gold standard and allows determination of mosaicism. The embryo biopsy revolution’s 30-year saga is still unfolding, and non-invasive genetic testing holds potential to revolutionize the way embryos are tested for genetic disorders.