How exactly is the PGD test done?
Gender is determined by our sex chromosomes. PGD testing is different than most genetic testing, since it is done on only one or two embryonic cells and must be completed within 48 hours to allow embryo transfer by Day 5. Since standard chromosome analysis takes several days, a different method called fluorescence in-situ hybridization (FISH) is performed. Each chromosome has unique areas of DNA present only on that chromosome. A small DNA probe is used to recognize these unique patterns and fluoresce, or light up, when it attaches to the chromosome. Each probe shines light in a different color, allowing several chromosomes to be tested at the same time. This technique is called FISH. FISH probes for X and Y are used to determine the gender of each embryo. For laboratory control a FISH probe for a different chromosome is also used, typically chromosome 21. The presence of these chromosomes are viewed simultaneously. A normal cell should show 2 FISH signals (or lights) for the numbered
