Preimplantation Genetic Diagnosis: Blastocyst Biopsy

Preimplantation genetic diagnosis is a groundbreaking technique to identify genetic defects in embryos from IVF procedures. The procedure is performed by obtaining a cell from the embryo; this cell is analyzed. The removal of the cell can be performed through one of three techniques: polar body biopsy, cleavage stage embryo biopsy or blastocyst biopsy. The cleavage stage biopsy is the most popular.

Blastocyst Biopsy

The blastocyst biopsy can be performed on blastocysts, which form the fourth day after the egg is obtained. The procedure is performed by making a hole in the zona pellucida of the egg, and a tiny biopsy pipette will retrieve a cell.

The procedure will not affect the inner mass cell of the embryo, so that this will not be damaged. However, a fertility doctor that is experienced in cell micromanipulation should perform the procedure, to make sure that the embryo stays undamaged. Special microscopes and tools are used during the blastocyst biopsy. After the cell is obtained, the embryo will be returned to the incubator. The obtained cell can be analyzed employing the FISH or the PCR technology.

Disadvantages of Blastocyst Biopsy

The blastocyst biopsy may fail to provide a cell that carries essential information. For instance, if the biopsy extracts a cell from the trophotoderm, these cells present a high level of mosaicism (several cell lines) and may give mixed results that may not be conclusive.

The biopsy is performed starting from five days after the egg retrieval; given that the aneuploidy test can only be performed 24 to 48 hours after the biopsy and the fact that the embryo may not survive more than six days, the blastocysts that have been biopsied need to be frozen.

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