ABSTRACT
In the mid-1980s, the development of polymerase chain reaction (PCR) strategies for amplification of specific fragments of DNA from single cells1-3 paved the way for preimplantation genetic diagnosis (PGD) of inherited disease using one or more cells biopsied from embryos at preimplantation stages after in vitro fertilization (IVF).4 As the human oocyte and embryo up to the expanded blastocyst stage are enclosed within the zona pellucida, any sampling procedure requires micromanipulation to penetrate this protective glycoprotein layer. The second challenge is to remove the target cells with minimal damage to the embryo, again requiring micromanipulation. Various approaches have been advocated from biopsy of polar bodies at the zygote stage to removal of some of the outer trophectoderm (TE) cells from blastocysts, and each has particular advantages and disadvantages (Table 14.1).5
