Preimplantation genetic diagnosis/screening (PGD-PGS)
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View all ProgramsWhat is preimplantation genetic diagnosis (PGD)?
Embryo morphology is not accurate to detect the most viable embryos. One of the main reasons why good quality embryos fail to implant is because of their genetic status. PGD is a technique, which enables couples with a particular inherited diseases in their family to avoid passing it on to their children. PGD is performed on embryo to determine if it has also inherited the genetic or chromosomal abnormality.
One or more cells from an embryo are tested for the presence of a gene or genes that may harm the embryo and developing child, correct number of chromosomes, and translocation of a piece (or more) of chromosome from one to another chromosome.
For PGD is used the embryos which are created by assisted reproductive technology (ART). Up to two unaffected embryos are transferred to the woman’s uterus for implantation. If successful, the procedure will result in healthy pregnancy.
There are three types of biopsy:
- Polar Body Biopsy (Egg screening)
With this form of PGS the polar body is removed from the unfertilised egg. The polar body is not necessary for successful fertilisation or normal embryonic development and therefore this should have no deleterious effect on the embryo. The removed genetic material can then be analysed to determine whether there are any genetic abnormalities.
- Day 3 Biopsy (Blastomere Biopsy)
Blastomere biopsy is normally performed on the third day after fertilisation when the embryo has reached a 6-8 cell stage. In order to remove 1 or 2 cells containing a nucleus of the embryo, a hole has to be made in the zona pellucida. The advantage of sampling at this stage of development is that the genetic material of both parents can be examined. However, there is an increased chance of chromosomal mosaicism at this stage of development. This means that the cell that is removed and examined, may not be the same as the other cells of the embryo and a false result can be obtained. The result of the biopsy is known within a two weeks
Removing a cell from a day 3 embryo appears not to have a detrimental effect on the embryo development into a perfectly normal baby. It is not known at this time whether biopsied embryos have a lower chance of implantation than embryos without biopsy.
- Day 5 Biopsy (Blastocyst Biopsy)
With a day 5 biopsy, several cells can be taken from the outer layer of the developing blastocyst (trophectoderm). These are the cells, which form the placenta. Studies have shown that this is not detrimental to the development of the embryo. By removing several cells, the accuracy of the test can be improved. One disadvantage of performing the test at this time is that the number of blastocysts available for sampling may be reduced in older patients or has connection with bad morphology of blastocysts. In addition, delaying the biopsy to this late stage of development limits the time to perform genetic studies. In this case, the blastocysts should be frozen and will be used in the next cycle.
An in vitro fertilization cycle with PGD involve:
- IVF procedure
- Biopsy
- Laboratory analysis
- Freezing/thawing of embryos
- Transfer
What are advantages of PGD?
It is an alternative to:
- prenatal diagnostic testing: Couples avoid the stress during pregnancy associated with diagnosis.
- termination of pregnancy: termination of pregnancy: when prenatal testing (amniocentesis or chorionic villus tests) reveals a genetic abnormality
The opportunity to conceive a pregnancy that is biologically the parents’ own and yet unaffected by a genetic condition in the family
What are disadvantages of PGD?
The process of IVF and PGD poses some risks to the woman and the embryo:
- Health risks of the IVF cycle An embryo may not develop after fertilization of an egg
- Not all embryos will be suitable for biopsy
- The embryo may not develop after biopsy
- There may not be any unaffected embryos available for transfer
- Test results may be inconclusive
- Results are not 100% accurate
- No pregnancy is achieved, even after the transfer of an unaffected embryo
What is preimplantation genetic screening (PGS/PGT-A)?
Preimplantation genetic screening (PGS) is used to detect chromosomal abnormalities and chromosomal rearrangements (translocations, inversions, deletions, etc) and to test for the number of chromosomes. This is also known as aneuploidy screening. The percentage of abnormal genetic embryos during IVF treatment is relatively high when patients are over 38 years (around 50-60%). Thus, PGS is used to detect chromosomal abnormalities and chromosomal rearrangements (translocations, inversions, deletions, etc). Embryos that have a normal number of chromosomes are more likely to result in a viable pregnancy.
Pre-implantation Genetic Testing Aneuploidy (PGT-A). A genetic test where an embryo is biopsied and tested for chromosomal abnormalities (aneuploidy). Aneuploid embryos are believed to be the leading cause of miscarriages.
The basic idea behind PGS is that embryos that have the right number of chromosomes (euploid) have better success than embryos with the wrong number of chromosomes (aneuploid). Nearly every cell in our body has DNA and for the most part it’s just bundled up together in a mess.
When the cell divides to copy itself, it organizes this mess of DNA (called “chromatin” – it looks like a bunch of spaghetti) into chromosomes. It does this because it’s easier to make copies of the DNA this way.
We have 46 chromosomes – 23 come from Mom and 23 from Dad. 22 of these are “autosomes” (#1-22) and 2 are sex chromosomes (X and Y). So there’s 24 different chromosomes that contain all the information for life.
The sex chromosomes determine gender:
- A girl has two copies of the X chromosome.
- A boy has a copy of X and a copy of Y.
- Chromosomal aneuploidy is when there’s any number other than 46. So if you have 45, or 49, then that’s aneuploid. An embryo with 46 chromosomes has the correct number and this is euploid.
When your embryo is aneuploid, it has a higher chance of miscarrying, or not implanting.
Gender Selection. Family Balancing
Gender selection is an ivf technique used by intended parents who wish to choose the sex of their baby. The embryos with the desired sex are then implanted into the woman’s uterus. Gender of embryos is defined by the PGS testing. Gender selection is also called "Family Balancing". It's used by prospective parents, when they have a strong desire to complete or “balance” their family according to their own personal plans.
What is the cost of gender selection?
The cost of PGS of 1 embryo is 570 EUR. Only high quality embryos of the desired sex are transfered.