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Preimplantation Genetic Screening (PGS)

Preimplantation Genetic Screening (PGS)

PGS stands for Preimplantation Genetic Screening and it is a medical technique that helps the patient to select healthy embryos by identifying some chromosomal defects and doctors can only transfer back the healthy embryos back into the woman’s uterus. The PGS and the PGD are related to each other, both are examination process that determined genetic disorders.


What is preimplantation Genetic Screening PGS?

Parents who have no evidence of carrying genetic disorders can use PGS as a preventative measure to identify any chromosomal abnormalities. The cells of an egg will be undergoing a screening analysis and chromosomes examination to search for any potential genetic abnormalities. This screening effectively decreases the risk of miscarriage and failed transfer processes during IVF.


What is the difference between PGD and PGS?

Genetic testing is divided into two methods, the PGD and the PGS, but what are the differences and similarities. Both techniques are used during the IVF and ICSI procedure. the PGD is used when one of the parents or both are aware of having a genetic disorder that may pass by to their child. So, they examine their embryos' cells to pick up the healthy ones. PGD which stands out for preimplantation Genetic Diagnosis allows doctors to discover Genetic diseases before embryo implantation process and pregnancy followed by.


PGS method is used to find out if any of the parents have a genetic disorder that may be passed by to their children. In this case, there is no specific known potentially genetic disorder recognized by the parents, unlike the PGD which a specific disorder is known and wanted to be avoided. The two testing methods help doctors to diagnose down syndrome, cystic fibrosis, fragile-x, hemophilia, spinal muscular atrophy, sickle cell anemia, and other genetic diseases.


Who should have PGS?

Parents with no known genetic inherited diseases should go for preimplantation genetic screening to see if they have any and prevent them from passing to their child. We also highly recommend having PGS in the following conditions:

  • Women who older than 38 years old.
  • Couples who had failed IVF or ICSI.
  • Couples who have a history of pregnancy lost (recurrent miscarriage).
  • Couples who want to select the gender of their embryo.
  • Couples who have their eggs, sperms, embryos frozen.


How PGS is performed?

PGS provides information about chromosomes in the embryo cells. Chromosomes are made of DNA which contains the code of how we develop, grow, and function. Each cell should have 2 pairs of chromosomes, one of the sperm and one of the eggs. The process of PGS if there any extra or missing chromosomes in the embryo.

  • As we mentioned that the Genetic testing methods are done during ICSI and IVF procedures. So, when the egg is fertilized, it is left in incubators to divide into many cells. After 5-6 days, the embryo reaches the blastocyst stage which maintains 100-200 cells.
  • A 4-6 cell biopsy is taken from the embryo to be screened in the lab when developing into the blastocyst stage.
  • The biopsy is sent to the genetic lap to be examined and screened by the PGS technique.
  • The screening process analysis each embryo biopsy and counts the number of chromosomes in each sample. The normal number of chromosomes should be 46 in each cell or 23 pairs in total.


PGS advantages:

PGS or Preimplantation Genetic Screening has benefits as the woman gets older and has a chance of conceiving decreases and the chance of miscarriage increases (usually happens to women over 35 years old). Women between 35 to 38 are having higher risks of miscarriages, and PGS could be helpful to such a group as it improves their chances of getting pregnant.

PGS testing gives the patients two additional months to. Instead of having one month to implant back the embryo to the uterus, they will have extra time until the PGS process is done. This could be an advantage for some patients.


PGS disadvantages:

  • Some patients do not come up with Embryos that suitable for PGS and biopsy can’t be taken, and that doesn’t mean it could not be transferred, you can complete your ICSI or IVF anyway.
  • There is a small chance that PGS results are not correct.
  • There is a small chance that the embryo may be damaged during the process of PGS and the leftovers cannot survive the freezing process after.
  • PGS results are complicated and in most cases the results are clear and you will have one or two euploid embryo.
  • Sometimes the results are not clear if the embryo is genetic disorder free or not. In such cases, the doctors will re-biopsy or transfer the embryo after discussing the chances and risks with the patients. 


Note: all of the mentioned disadvantages depend on the history and case of every patient