Firstly, a hole is made in the pellucid zone (a.k.a. egg coat) using a laser or using hyaluronidase from the embryo, and then the cell or blastomere is aspirated.
After that, a chromosomal analysis of the cell is performed at the genetics laboratory by means of a technique called FISH or with microarrays, a technique which allows a massive analysis of genetic disorders.
PGD is a complex technique used by expert biologists.
At this early stage of embryo development, its cells are totipotent stem cells, that is to say, they can differentiate into any cell in the human body until a whole organism is developed.
Thus, performing a biopsy on a cell from the embryo won’t cause any problem on its development, which will finish when a whole human being is formed.