The biopsy and analysis of the first and second polar bodies can be completed before fertilization, which is the moment from which the zygote is generally considered[who?]
[3] The main advantage of the use of polar bodies in PGD is that they are not necessary for successful fertilisation or normal embryonic development, thus ensuring no deleterious effect for the embryo.
Another drawback is the increased risk of diagnostic error, for instance due to the degradation of the genetic material or events of recombination that lead to heterozygous first polar bodies.
When the majority of errors occur in chromatids rather than entire chromosomes (a condition correlated with the age of the mother), screening only the first polar body will fail to detect a large percentage of defective eggs.
[3] Because euploid polar bodies contain the same chromosomes as the oocyte, they can be used as a source of genetic material that is easily accessed without destroying the egg.