PGD refers to the technique of evaluating an individual cell taken from an embryo for genetic abnormalities. PGD requires the use of in vitro fertilization to produce growing embryos. Then, 1 cell is removed from each 6-10 cell embryo. Each isolated embryonic cell (“blastomere”) is prepared and tested for its chromosome make-up and, if needed, specific genes. Unfortunately, for technical reasons, FISH is limited to staining only 12 of the 24 chromosomes (22 chromosome pairs plus the sex chromosomes, X and Y) so not all abnormal embryos can be identified. The embryos with abnormal chromosomes are discarded.

Two different genetic assessment techniques yield the diagnostic information necessary to decide which embryos to transfer.

1. FISH (Fluorescence In-Situ Hybridization) refers to the technique of “painting” the whole cell with specific probes bound to a colored marker. FISH allows us to count the number of chromosomes stained with each probe thus determining how many of each chromosome is present. A normal embryo will have two stained chromosomes for each probe. If only one stained chromosome is seen, then one chromosome is missing (“monosomy”). An example is “Turner’s Syndrome” in which one X chromosome is missing. Or, if three stained chromosomes are seen for a probe, then one extra chromosome is present (“trisomy”). An example is “Down’s Syndrome”, a trisomy of chromosome #21. Unfortunately, for technical reasons, FISH is limited to staining only 8-10 of the 23 chromosome pairs in the cell so not all abnormal embryos can be identified. Those chromosomes most likely to be found abnormal or result in live-born abnormal children are tested.
    
2. PCR (Polymerase Chain Reaction) refers to the technique of splitting chromosomes into pieces and then looking for normal and abnormal chromosome fragments. PCR works well to help us identify specific gene disorders but does not help us identify the number of chromosomes present.

We offer PGD in indicated cases. We partner with one of the pioneers in PGD technology; Dr. Santiago Munné (Reprogenetics, Inc., www.reprogenetics.com) whose laboratory performs the PGD analysis of the embryonic cells.