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Preimplantation genetic testing for aneuploidies (PGT‐A)

Preimplantation genetic testing for aneuploidies (PGT‐A), formerly known as preimplantation genetic screening (PGS), is an alternative method to select embryos for transfer in IVF. This test identifies the preimplantation embryos with a normal chromosome complement (euploid) during IVF. PGT-A improves pregnancy success by sifting out embryos with an abnormal chromosome copy number.

What are the reasons to do PGT-A?

Embryos with normal chromosome copy numbers have the potential to implant and reach full-term pregnancy resulting in the delivery of a healthy baby. Most of the time, it is difficult to identify the normal embryo visually using a microscope. The normal appearance of an embryo cannot confirm the absence of genetic abnormality in that embryo. Hence, PGT-A helps to select the embryos with a normal chromosome number. 

Who should consider PGT-A?

PGT-A is considered in women who 
•    Had a history of recurrent miscarriage
•    Experienced recurrent implantation failure
•    Had a prior pregnancy with a chromosome abnormality 
•    Are in their mid-thirties or older

How and when is PGT-A done?

PGT-A is performed on a few cells taken from the embryo. Hence, the biopsy procedure has two steps: 
•    the opening of the zona pellucida (outer shell of the embryo)
•    removal of the cell(s).
The biopsy is performed either at the cleavage stage (day 3 of embryonic development) or the blastocyst stage (starting from day 5 of embryonic development). A 3-day old embryo has nearly 6 to 8 cells whereas a blastocyst has a few hundred cells. Therefore, several cells can be safely removed during the biopsy of a 5-, 6- or 7-day old embryo. The cells of the embryo will be tested using the NGS technique allowing comprehensive chromosome screening. 

How safe is PGT-A?

It is a safe procedure. The process should be handled correctly by a skillful embryologist and then the embryo develops normally even after the embryo biopsy.

Does PGT-A assess all genetic diseases?

PGT-A testing can only assess numerical changes in chromosome number and other imbalances in genetic material including deletions (part of a chromosome is missing) and duplications (part of the chromosome is doubled).

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