What is PGS?
Preimplantation genetic screening (PGS) determines the chromosomal status of an embryo by screening all 23 chromosome pairs prior to transfer in an IVF cycle. PGS testing helps doctors and patients decide which embryos to transfer. The procedure allows us to analyze all 24 chromosome types in order to discard the possibility of chromosome aneuploidy before implantation
It should be noted that PGS has been called different things but they are all describing the same procedure. You may hear these terms used interchangeably.
- PGD for aneuploidy screening (PGD-A)
- Comprehensive chromosome screening (CCS)
Benefit of PGS
It is estimated that half of human fertilized embryos carry the wrong number of chromosomes, which is a leading cause of spontaneous miscarriage. The risk of having a chromosome abnormality in a natural pregnancy increases with a woman’s age, and there is risk even in young women.
There are two sex chromosomes (X and Y) and 22 other non-sex chromosomes. Normally there are 23 pairs of chromosomes in each human cell. A numerical change in the number of chromosomes is called aneuploidy. Aneuploidy is responsible for the vast majority of spontaneous miscarriages and can result in birth defects and mental retardation in live born babies. Most types of aneuploidy are not compatible with life. Chromosomal abnormalities are a major cause of the failure of embryos to implant, and of miscarriages.
From a study at Beloved Fertility Center, the chance of a woman younger than 35 years old to have a chromosome abnormality is at least 35%, and the incidence will increase with the woman’s age. This is why a woman’s age is critical when considering the probability of getting pregnant. Chromosomal normal embryos are the most likely to develop to term and to be born as a healthy baby.
These are the following individuals who are more likely to benefit from PGS:
- Women over the age of 35
- Women who had 2 or more miscarriages
- Women who had 3 or more unsuccessful IVF cycles before
- Women who had a previous pregnancy with whole chromosome abnormality
- Men who have male factor infertility
- Individuals who would want to know the gender of their child to avoid to transfer the affected child with the specific sex.
- Individuals who want to reduce the chance of having twins or multiple births
PGS to select healthy embryos with the correct number of chromosomes does the following:
- PGS for 23 chromosome pairs eliminates negative effect of maternal age on implantation and increases the chance of a healthy pregnancy across all age groups. It means that older women who transfer chromosomal normal embryos, the chance of pregnancy is the same as younger women who transfer chromosomal normal embryos.
- Reduces the likelihood of miscarriage.
- Allows for confident single-embryo transfer, which helps avoid the added health
The process of PGS composes of:
- IVF/ICSI process
- Blastocyst culture ( 5-6 days stage embryo)
- Blastocyst biopsy for obtaining an embryonic DNA for testing
- Blastocyst Cryopreservation (Freezing)
- Frozen embryo transfer