Used in conjunction with in vitro fertilization, PGD (Preimplantation Genetic Diagnosis) helps increase the likelihood of selecting genetically normal embryos to transfer to the uterus. PGD involves the microsurgical removal and biopsy of one cell from a six- to eight-cell embryo. The genetic diagnosis of the cell can be done by using either PCR (polymerase chain reaction) or FISH (fluorescence in situ hybridization), depending on the indication for PGD. By prescreening a cell from each day-3-embryo, the healthiest embryos with the greatest potential for implantation can be identified.
What does PGD accomplish?
Preimplantation genetic diagnosis has been shown to be helpful for specific groups of patients. Women with recurrent miscarriage due to chromosome issues have been shown to have higher implantation rates and lower spontaneous abortion rates when PGD is used with IVF. In addition, carriers of single gene disorders (e.g. cystic fibrosis, thalassemia) benefit from prescreening their embryos before they are transferred. PGD for gender selection (family balancing) in sex-linked disorders is also routinely used to improve chances for a successful outcome (i.e. having an unaffected pregnancy). By identifying the sex of the embryo, sex-linked disorders — such as hemophilia — can be avoided. The benefit of PGD is less clear in other patients, including those with unexplained infertility, advanced maternal age or repeat IVF failure.
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The biopsy of the embryo and subsequent molecular analysis of the blastomere are both technically demanding and complex procedures that require highly trained laboratory personnel. Genetic results are usually reported within 2-3 days of the biopsy, followed by the subsequent transfer of unaffected embryos.