In some cases, genetic testing of embryos is required in IVF treatments. The general name of these methods is Preimplantation Genetic Diagnosis (PGD) or Screening. If a known genetic disease or chromosome disorder is to be investigated, the abbreviations PGD/PGT are used, and if general screening is to be performed, the abbreviations PGS are used. …
In some cases, genetic testing of embryos is required in IVF treatments. The general name of these methods is Preimplantation Genetic Diagnosis (PGD) or Screening. If a known genetic disease or chromosome disorder is to be investigated, the abbreviations PGD/PGT are used, and if general screening is to be performed, the abbreviations PGS are used. We can roughly group the situations in which we need these tests under a few headings:
1. Recurrent IVF failures,
2. Recurrent miscarriages,
3. Detection of a chromosomal disorder in the mother or father candidate,
4. Knowing the presence of a genetic disease in the mother or father candidate or both.
Apart from these items, we also use it frequently in women who are 40 years of age and older and have high ovarian reserve, as it sometimes reduces the number and duration of transfers required to reach a healthy baby.
Before genetic analysis is performed on the embryos of a couple, both the man and the woman should be examined in detail and the necessary precautions should be taken. Otherwise, the probability of failure will increase even if the embryo transfer is made despite the test result being healthy.
General Information:
Basically, the path followed in tests performed to evaluate embryo genetics is the same at the beginning. IVF is performed, after the sperm and egg unite, the embryo is grown and a cell or cells are taken from the embryo and sent for genetic analysis.
However, details are important, if you take a single cell on the 3rd day of the embryo to evaluate the chromosome structure, you should know that the embryos are very highly mosaic in that period. In other words, most embryos consist of a mixture of healthy and abnormal cells in certain proportions. As a result, the chromosome result of the cell you take may not represent the embryo as a whole. For this reason, if we are going to perform chromosome analysis on embryos for a long time, we prefer 5th-6th day embryos. In these embryos at the blastocyst level, the probability of mosaic structure is lower and it is possible to take a larger number of cells and send them for analysis – without damaging the embryo. This makes the future result more reliable.
Methods:
Another important factor is the method used to evaluate the chromosome structures of embryos. In the past, a single cell was taken from the embryos on the 3rd day and the number and structure of the chromosomes stained with fluorescent dyes were evaluated under a microscope. Although we have many babies to whom we owe this method called FISH, the reliability of the method was not very high. This disadvantage was due to the biopsy performed on the 3rd day, the possibility of error due to staining and most importantly, the fact that it could only scan 7-9 of the 24 types of chromosomes.
We started to get much more detailed and reliable results with the comprehensive chromosome screening methods that we started to use frequently since 2012-2013. In these two methods called aCGh and NGS, 7-8 cells are taken while the embryos are in the blastocyst stage, the method is based on examining the DNA obtained from the cells rather than staining, and all 24 chromosomes (X and Y chromosomes separately) can be examined with very high reliability.
Due to these developments, we no longer perform screening with the 3rd day biopsy and FISH method. This method may still be required only in some special cases and these situations are gradually decreasing over time.
If there is a chromosome problem in the woman and/or man (translocation, inversion, etc.), we can still perform screening mostly by using these new generation methods.
In some couples, there may be a genetic disease or carrier status. In the presence of diseases such as cystic fibrosis, Mediterranean anemia, or in general, any disease where we know the address of the gene that causes the disease, it is possible to screen for that disease in embryos after in vitro fertilization treatment and place healthy embryos in the uterus.
With genetic tests performed on embryos, pregnancy rates per transfer increase and miscarriage rates decrease significantly. Although the reliability of these tests increases day by day, it is important to confirm the result with invasive or non-invasive genetic diagnosis tests that can be performed when pregnancy occurs.
