The laboratory testing procedures take place in a special laboratory where all conditions are sterile. The egg cell prior to fertilization divides into two unequal cells. 

The larger cell is the mature egg that will be fertilized.  The smaller cell (called a polar body) can be removed and tested for its genetic composition by a procedure called polar body removal.

A semen sample is provided to the laboratory on the day of the egg retrieval.  The sample is then processed in order to obtain an optimum sample for fertilization.  In most cases, a single sperm is injected into the egg by a procedure known as intracytoplasmic sperm injection or ICSI. 

At this time, a second polar body is released from the egg. The eggs will be fertilized using ICSI to maximize the rate of fertilization and to monitor the exact timing of polar body removal.

Occasionally, fertilization does not occur, or occurs abnormally (which occurs to fertile couples as well). After fertilization has taken place, the embryo is transferred to a special growth medium.