Polar bodies are the product of meiotic division of female gametes and contain 23 maternal chromosomes (1st polar body) or 23 maternal chromatids (2nd polar body). Therefore, when examining polar bodies, only the maternal chromosomal composition of the future embryo is tested.

The 1st polar body can be extracted from a mature egg (on day 0 of embryonic development) and the 2nd polar body from a successfully fertilized egg/zygote (on day 1 of embryonic development).

In PGT, both polar bodies must be examined independently, and based on the results of their examination, the genetic finding in the corresponding oocyte is determined ("predicted").