PGT Procedure

PGT can only be performed on embryos in vitro (in a laboratory). That means this test is always performed in conjunction with an in vitro fertilization cycle.

In Vitro Fertilization (very brief summary)

Medication is given to stimulate the production of multiple eggs.

• Egg retrieval is performed using an ultrasound guided needle.
• Eggs are then mixed with the partner’s sperm in the IVF Laboratory and placed in the incubator for fertilization and embryo growth.
• Embryo biopsy may be performed after 3 days in the laboratory, followed by a “fresh” embryo transfer 2 days later.
• In some cases, the biopsy will be performed after 5-6 days in the lab, at the blastocyst stage. These embryos are then frozen and transferred in a subsequent cycle.

Embryo Biopsy

To enable screening of a human embryo before transfer to the uterus, it is necessary to remove cell(s) so that the genetic material can be analyzed. It must be noted that in routine genetic analysis there are usually hundreds of cells available for processing; however, with embryo biopsy only one to several cells are commonly available, and they must contain a nucleus with chromosomes present to determine the genetic status of the rest of the embryo. The biopsy method is relatively straightforward, but this does not mean that it is an easy procedure to undertake.

Other Issues

Misdiagnosis

Misdiagnosis can occur due to mosaicism within the embryo. Some embryos may contain blastomeres (cells produced by the cleavage [division] of a fertilized egg) which are genetically normal and, within the same embryo, other blastomeres which are abnormal. This is called mosaicism. For this reason, a diagnosis may be incorrect. This may result in the transfer of an embryo carrying a chromosome abnormality or the failure to transfer a normal embryo.

Experimental error can also account for a misdiagnosis. Improper cell fixation techniques, DNA denaturation errors, allelic drop-out or amplification of contaminated DNA can lead to a wrong diagnosis.