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PreImplantation Genetic Screening (PGS) is not a stand-alone treatment method. It is used to screen the chromosomes of embryos formed during an IVF cycle. If preimplantation genetic screening (PGS) is required for an IVF treatment, the procedure will be identical to standard IVF/ICSI treatments. Before the embryos are transferred into the uterus, they are biopsied so that they can be screened genetically.
PGS stands for Preimplantation Genetic Screening and the aim is to screen the patients’ embryos for chromosomal aneuploidy. This method is used for gender selection or for checking the embryos’ chromosomes in order to give patients a higher chance of success in IVF especially in older age brackets.
PGD stands for PreImplantation Genetic Diagnosis. It is used as a “diagnostic” tool for patients with a known genetic disorder and at risk of transferring a genetic disease to their offspring. With the help of Pgd, specific genetic disorders in embryos can be diagnosed and only embryos without a genetic disorder are transferred to the uterus.
PGD is recommended for the following frequently observed conditions:
Due to Northern Cyprus IVF laws and “ethical” concerns, PGD cannot be used alone as a gender selection method for family balancing. The reason is without other gender selection methods, most of the embryos will be of “undesired” sex and will be destroyed once PGS is performed. To prevent this, PGS has been banned as a gender selection method for family balancing. However, it can still be used for choosing the sex of the baby in case of X-linked genetic diseases.
PGS can also be used for family balancing if gender selection is done via MicroSort. With this procedure, desired gender’s embryos will be created through IVF and no embryos will be destroyed because of being the wrong gender. In this case, we use PGS as a screening method for embryos’ chromosomes to ensure that we only transfer healthy embryos to the uterus.
Patients opting for Gender Selection (IVF + PGS) will have to undergo some tests so that our team can evaluate the fertility levels of the couples and decide which treatment protocol is suitable according to the test results.
We will be able to make an assessment of your fertility levels and identify the right medication regimen based on the test results.
Depending on the specific purpose why PreImplantation Genetic Screening (PGS) is required in the first place, there are several different methods that can be used:
FISH: During an IVF cycle, Fluorescent in situ hybridization is the simplest screening method used to determine the chromosomal contents of embryos formed. FISH method can be employed on polar body biopsies, blastomeres and trophectoderm biopsies. With the FISH method, the biopsied cells are fixated on a glass slide and are hybridised using DNA probes. These probes are for specific chromosomes and they are labeled with a fluochrome. 5-chromosome probe is the most common FISH analysis where chromosomes X, Y, 13, 18 and 21 are screened. 90% of genetic abnormalities observed at birth are caused by these chromosomes. FISH can be a sufficient screening method for major genetic disorders and for gender selection.
Array CGH: Rather than a limited number of chromosomes, Array Comparative Genome Hybridization (CGH) goes one step further and analyzes the entire chromosome content of the biopsied cell. The Array CGH has several probes for each of the 24 chromosomes found in humans. Because of this reason, it is possible to simultaneously screen multiple locations on each and every chromosome. The array CGH method can also be used to test chromosomal translocations and other abnormalities.
PGS is used for screening chromosome abnormalities as well as gender selection. It should be noted that, even if you are young and healthy, some of your embryos are likely to have genetic problems associated with them. As age gets older, genetic defects of embryos will be much higher. Prevalence of genetic problems in embryos will be more pronounced, especially after 35 years of age. The figure below shows the incidence of genetic abnormalities in embryos based on maternal age:
According to a large scale study on embryos of women aged between 30 and 44, it has been shown that approximately 25% of all the embryos of a 30 year-old woman would have genetic defects.
At the age of 35, this rate goes up to 32% and at the age of 44, this rate goes up to higher than 70%. These numbers shows how important PGS screening is in IVF treatments after 30 years of age.
Next generation sequencing (NGS) is the latest technology in embryo screening methods. North Cyprus IVF Center proudly offers NGS to its patients as the SOLE owner of “Next Generation DNA Sequencing” in entire Cyprus and 1 in 10 clinics in the world.
Up till now, FISH or CGH array methods were the only methods to screen embryos for chromosomal aneuploidies and neither method would successfully identify mosaicism. Next generation sequencing goes one step further and allows for an in-depth analysis of all the embryos produced during the IVF cycle before they are transferred into the uterus.
NGS is superior to array CGH since it has the ability to detect mosaicism in embryos. Mosacism is observed when embryos’ cells have different genotypes. Next generation DNA sequencing can determine if an embryo has mosaicism and which chromosome is affected.
With the use of next generation DNA sequencing, we are now able to select the “healthiest” embryo for transfer and minimize the likelihood of a miscarriage due to a genetic disorder.