ABSTRACT
The rst report of the application of trophectoderm biopsy for the purpose of determining the genetics status of blastocyst-stage embryos was the sexing of rabbit embryos by Edwards and Gardner in 1967 [1]. Decades later and following in the wake of the development of human in vitro fertilization (IVF), Handyside and coworkers reported the rst live birth after embryo biopsy in 1990 [2]. As preimplantation genetic diagnosis (PGD) developed, it was typical for biopsy to be performed to remove either the polar bodies or blastomeres. Polar body biopsy required the removal of the rst and second polar bodies across Day 0 and Day 1 of development, the obvious restriction with polar body analysis being that only maternally carried genetic anomalies would be revealed. Blastomere biopsy occurred on Day 3 postfertilization when the embryo had progressed to the six-to eight-cell stage and typically resulted in the extraction of one or two blastomeres. Both polar bodies and blastomeres were analyzed by either polymerase chain reaction (PCR) or uorescent in situ hybridization (FISH) techniques. PCR required the design of oligonucleotide primers to amplify allelic targets such a deletion or insertions in a single cell or polar body. FISH targeted and labeled chromosomes in a single cell, allowing detection of chromosomal aneuploidies and translocations. Recently, comparative genome hybridization (CGH) has displaced FISH for the purpose of chromosome aneuploidy and translocation analysis in PGD. To remove either the polar bodies or blastomeres from the embryo, the zona pellucida was breached by either mechanical means or by dissolving the protein with acid Tyrode’s solution, and the embryo may or may not have been incubated for a period of time in a calcium-and magnesium-free medium to decrease cell-to-cell interactions and therefore make the biopsy of cells easier. During the late 1990s, the development of near-infrared lasers allowed for a more rapid and controllable opening if the zona pellucida.
