Preimplantation Genetic Diagnosis (PGD) is an adjunctive procedure to IVF starting with embryo biopsy which can be performed on day 3 or day 5 of development. This technique employs molecular genetic methods to enable the identification of genetically normal embryos, prevention of genetic disease as well as to aid in the identification of the gender of the embryo. This method is important for individuals or couples who have selected a particular gender for the child in case of sex-linked disease.
“This technique employs molecular genetic methods to enable the identification of genetically normal embryos, prevention of genetic diseases”
The embryo cells can be tested by SNPs (Single Nucleotide Polymorphism) analysis which simultaneously measures intensity differences and allelic ratios of embryo cells. SNPs analysis can be used to detect 24 chromosomes aneuploidy, translocation or Inversion of chromosomes and single gene disorder.
Another technique is FISH (Fluorescence in Situ Hybridization) which examine the cells under a fluorescent microscope. These cells are then hybridized with DNA 5 color probes, 13, 18, 21, X and Y labeled with different flurochromes. The numbers of chromosomes of each type in the specific cell are counted to differentiate normal cells from cells with aneuploidy. This method is useful in gender selection for X-linked diseases and for women with advanced maternal age which entail higher risk of having children with Down´s syndrome or suffering recurrent miscarriages.