Since the test relies on visualizing little colored spots under the microscope, it is not possible to study every chromosome. Rare abnormalities involving other chromosomes can be missed, but fortunately, these embryos almost never progress to the fetal stage. Since polar body biopsies only evaluate the genetic material from the egg, the sex of the embryo cannot be determined from this procedure. Also, aneuploidy resulting from a chromosomally abnormal sperm cannot be detected by analyzing the polar bodies. Sometimes, for technical reasons, the polar body biopsy does not provide clear information regarding aneuploidy, and a blastomere biopsy may be performed to clarify the results.
Sex determination requires a blastomere biopsy.
This slightly more invasive procedure requires removal of one or two of the early embryonic cells at the 6-8 cell stage, on day 3 after the egg retrieval. The second type of PGD seeks out single gene disorders. Different expressions of a single gene are known as alleles. A large library of genetic probes has been created that can specifically identify different alleles at specific gene sites that cause many genetic disorders. In some conditions, there are many different possible mutations of the gene, and specific probes for each patient are created.