{"id":2806,"date":"2023-10-23T21:55:16","date_gmt":"2023-10-23T11:55:16","guid":{"rendered":"https:\/\/www.drseragyoussif.com.au\/?page_id=2806"},"modified":"2025-01-16T05:48:25","modified_gmt":"2025-01-15T19:48:25","slug":"preimplantation-genetic-diagnosis-pgd","status":"publish","type":"page","link":"https:\/\/www.drseragyoussif.com.au\/?page_id=2806","title":{"rendered":"Preimplantation Genetic Diagnosis PGD"},"content":{"rendered":"
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Preimplantation Genetic Diagnosis PGD<\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n
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Definition<\/strong><\/h4>\n<\/div>\n<\/div>\n<\/div>\n
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Pre-implantation Genetic Diagnosis (PGD) is performed in conjunction with in vitro fertilization (IVF). PGD detects the genetic abnormalities either at gene level <\/span>or at chromosome level before transferring the embryo into the uterus to avoid the transfer of genetically affected embryos. PGD is offered for three conditions:<\/span><\/p>\n


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  • GD for Aneuploidy Screening<\/span><\/li>\n
  • PGD for single Gene Defect<\/span><\/li>\n
  • GD for Chromosome Translocatio<\/span><\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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    PGD for Aneuploidy Screening (PGD-AS)<\/strong><\/h4>\n<\/div>\n<\/div>\n<\/div>\n
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    PGD-AS is the most common type of PGD analysis. The embryos are tested using a panel of chromosomes that are commonly involved in miscarriages or trisomy pregnancies. Embryos screened this way and reported as normal have a higher rate of implantation, lower spontaneous loss and a reduced risk of trisomy offspring (e.g., Down\u2019s syndrome).<\/span><\/p>\n

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    • A normal human cell contains 46 chromosomes or 23 pairs of chromosomes. These chromosomes are string like structures that resides in the nucleus and carry the genetic information.<\/li>\n
    • Autosomes (22 pairs of chromosomes) are same in men and women. The 23rd pair of chromosome is called sex chromosomes. Women normally have two of the same sex chromosomes, called the X chromosome, while men normally have 2 different sex chromosomes, known as X and Y chromosomes.<\/li>\n
    • A Single Sperm contains half of the total number of 46 chromosomes or 23 chromosomes each i.e. 22X or 22Y.<\/li>\n
    • An egg contains half of the total number of 46 chromosomes or 23 chromosomes each i.e. 22X.<\/li>\n
    • A normal fertilized embryo is derived by the fusion of 23 chromosomes from an egg (22X) and 23 chromosomes from a single sperm (22X) or (22Y).<\/li>\n
    • Abnormal cell division in sperm or eggs might result in greater or fewer chromosomes than the normal 23. Therefore, any embryo that is derived from these sperm or eggs will carry extra or missing chromosomes, an abnormal condition referred as aneuploidy.<\/em><\/li>\n
    • In approximately, 70% of recurrent miscarriages abnormal numbers (aneuploidy<\/em>) of chromosomes are identified.<\/li>\n
    • Some of the most common chromosome abnormalities found in miscarriages are Trisomy<\/strong> (3 copies of chromosome) 16, 22, 21, 15, 18 or 13; Triploidy<\/strong> (3 copies of all the chromosomes); and abnormalities of the sex chromosomes i.e. additional or missing sex chromosomes.<\/li>\n
    • Chromosomally abnormal embryos usually:<\/li>\n<\/ul>\n
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      1. Fail to implant in the uterus<\/li>\n
      2. Miscarry<\/li>\n
      3. Develop and give birth to trisomy babies e.g. Down\u2019s Syndrome<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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        • The percentage of chromosomally abnormally embryos that each couple produces varies depending on their clinical status.<\/li>\n
        • Proportion of embryos that are abnormal is determined by<\/li>\n<\/ul>\n

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          1. Advanced Maternal Age (>35 years)<\/li>\n
          2. Number of Failed IVF cycles<\/li>\n
          3. Number of Miscarriages during normal conception<\/li>\n
          4. Quality of Sperm<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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            • Any deviation from having 2 copies of each chromosome is considered abnormal. If only one of two chromosomes is identified the embryo is considered monosomy <\/em>and if 3 chromosomes is identified it is considered trisomy. <\/em>Both these conditions are abnormal and not suitable for embryo transfer.<\/li>\n
            • For PGD-AS embryos created by IVF are cultured in the laboratory for 3 days to grow ideally to an 8-cell stage. At that point one or two cells are removed by making a hole on the outer shell of the embryo. This procedure is called embryo biopsy. The biopsied embryo is returned back to culture until the result for that cell\/cells are obtained usually on 5th day after egg retrieval.<\/li>\n
            • Removal of one or two cells from an eight cell embryo does not compromise the embryonic development.<\/li>\n
            • It is important that the embryo to be biopsied should have at least 5-cell and minimal fragmentation on the 3rd day of embryonic development. If the embryo contains too few cells, a biopsy might jeopardize the viability of the embryo.<\/li>\n
            • The nuclear material from the biopsied cell is tested with Fluorescent In- Situ Hybridization (FISH) to determine the chromosome status of each cell.<\/li>\n
            • A mixture of FISH probes in one or two sequential hybridizations is used. Possible chromosomes to be tested include 13, 15, 16, 18, 21, 22; X and Y. Abnormalities in these chromosomes are found commonly in miscarriages and abnormal live births.<\/li>\n
            • A normal cell should show 2 copies of FISH signals for each of the numbered chromosomes, and either 2X signals for females or 1X and 1Y signals for males.<\/li>\n
            • The PGD test result may not be obtained or is incorrect if:<\/li>\n
            • The cell is lost during fixation or nucleus is ruptured and no result will be available.<\/li>\n
            • The chromosomes in the nucleus fail to spread properly and lye on top of each other underestimating the number of chromosomes and can lead to a false result.<\/li>\n
            • FISH probe fails to bind to a chromosome suggesting a missing chromosome.<\/li>\n
            • Embryo biopsy occurs in the middle of cell division then the result appears to be two nuclei and four sets of chromosomes, FISH analysis from these cells can be difficult to interpret.<\/li>\n
            • PGD cycles are most successful when 8 or more embryos are created by IVF and at least 5 are of good quality based on the number of cells, fragmentation and uniformity in cell size.<\/li>\n
            • PGD usually does not increase the pregnancy rates but it reduces the miscarriages and the incidence of trisomy pregnancies.<\/li>\n
            • PGD is most successful in the patients who have more than 3 embryos that do not show abnormalities and at least two of them are developed to the blastocyst stage.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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              PGD for Single Gene Mutatio<\/h4>\n<\/div>\n<\/div>\n<\/div>\n
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