PGD / PDS (Preimplantation Genetic Diagnosis)
In IVF, we cannot know genetic health of an embryo while evaluating quality morphologically, even if the embryo looks good, well developed and in accordance with normal development schedule.
For this reason, by means called PGD, structural and quantitative anomalies can be detected, genetically healthy embryos are transferred, pregnancy rates are increased while miscarriage rates are decreased. In previous years only a limited number of chromosomes and a limited number of deseases were subject to scanning. But recent techniques
allows all chromosomes to be studied.
These techniques are applied to our patients in necessary conditions; usually, to repetitive miscarriages, severe male infertility, unsuccessful pregnancy despite large number of high quality embryo transfers, unidentified infertility cases and aged patients.
These techniques are applied not before third or preferably fifth day after fertilization. The decision have to me made considering quality of developed embryos and number of cells. Sample cells taken from embryos sent to
genetics laboratory for inspection.
Embryos with normal results are transferred. These procedures have to be carried out by personnel specialized on technical instruments. Various studies are possible in relation to patient characteristics. But due to serious financial burden, applications should be carried out when necessary.
ARRAY-CGH (Comparative Genomic Hybridisation)
Microarray technology which is used to analyze 24 chromosomes can inspect all chromosomes of embryo by connecting to chromosome couples of 4000 genetic indicators scattered throughout whole genome. But this can be
indirectly detected by comparison with a known normal DNA.
NGS (Next Generation Sequencing)
NGS is the latest and the most advanced PGD method in IVF. In this technique, DNA is enzymatically split up in millions of pieces after cloning. Quantitative inspection of chromosomes is considered over when DNA fractures are evaluated by a special algorythm. This technique potentially provides a more sensitive and precise inspection.
And quantity of mitochondria, which is the energy source of the cell can be detected and also genetic structure of necessary cell organelles for pregnancy is studied. This technique in addition, can detect low mosaicism up to 20% (50% for GH).
Single Gene Conditions
This PGD technique is used when couples are carriers of genetic conditions and there is risk of genetic transfer to children. Nowadays, almost all single gene conditions can be detected in embryo stage. This procedure is used for detecting prediagnosed condition rather than scanning embryo for various genetic condtions. Thalassemia, cystic fibrosis, SMA, hemophilia and others can be listed as examples to these conditions.
Cell-Free DNA Analysis
Trophectoderm cells from 5 day old blastocyst stage embryo are analyzed for PGD applications. It is still an invasive procedure although it is considered as safe. With this new technique to us, we genetically study blastocoel fluid extracted from embryo. In this manner, embryo’s genetic profile can be defined without a serious interference.