Preimplantation genetic screening (PGS) or Preimplantation genetic testing for aneuploidy (PGT-A)

The Genetic centre iVF Riga is currently the only one in the Baltic countries offering preimplantation genetic testing (PGT) or screening (PGS) of the embryos
PGS or PGT-A (preimplantation genetic testing for aneuploidy) is based on 3 key factors:

• Developed embryos are often aneuploid, which means that they have a changed number of chromosomes or chromosomal abnormalities, and the percentage of these issues increases with the woman’s age (see the table).
• Transfer of genetically incompetent embryos into the uterus does not result in a successful pregnancy.
• Unfortunately, the effect of chromosomal abnormalities on the embryonic morphology may be insignificant, which means that “nice-looking” embryos may be aneuploid.

Consequences:

If embryos are assessed only morphologically, there is a likelihood of selecting aneuploid embryos for the transfer into the woman’s uterus, because visually they look just as good or even better than other related embryos.

The transfer of genetically incompetent embryos results in no pregnancy or early pregnancy loss before the 12th week of gestation.

Furthermore, some chromosomal abnormalities are compatible with the development of the foetus, which may result in the birth of a child with Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or other chromosomal abnormalities, which are characterised by mental and physical retardation of the newborn infant.

Solution:

Genetic testing of developed embryos so that only those that only those with a bigger chance to implant in the uterus and also successfully continue their development are selected for the transfer.

This testing of embryos is called PGS (preimplantation genetic screening), or PGT-A (preimplantation genetic testing for aneuploidy) and it can be carried out using NGS method in iVF Riga Genetic centre.

NGS method (Next generation sequencing) allow for simultaneous testing of all chromosomes in an embryo before the embryo is transferred into the uterus, using reagents and equipment, developed based on the latest scientific achievements.

As a result, PGS by NGS makes it possible to choose the best and most viable genetically competent embryos, thus effectively increasing the rate of implantation, clinical pregnancy and successful birth.

Consequently, the testing of all chromosomes reduces the time and effort required to achieve the desired pregnancy, as it increases the likelihood of successful pregnancy after the first PGS (PGT-A) cycle, even if there have previously been several unsuccessful IVF cycles.

PGS (Preimplantation genetic screening) or PGT-A (Preimplantation genetic testing for aneuploidy)

Indications

High risk of the development of aneuploid embryos (with altered chromosome number) in case of parents with normal somatic karyotype:

• Women over 37 years
• Women over 35 years, if good morphology embryos develop, but pregnancy fails to occur
• Infertility of unexplained etiology in young couples
• Two or more unsuccessful IVF cycles (transfer of five or more embryos)
• A history of two or more spontaneous abortions (including the missed abortion)
• Decreased sperm quality of the partner (oligoasthenoteratozoospermia, severe oligozoospermia or azoospermia, poor sperm morphology, high DNA fragmentation)

In case of altered karyotype in parents (one or both) or if there is a high risk of passing a genetic disorder to the child:

• One or both parents are carriers of balanced chromosomal aberrations (Robertsonian or reciprocal translocations)
• Male infertility factor associated with AZF microdeletions (Y-chromosome)
• One or both parents are carriers of X-chromosome mutation (risk of development of e.g. Duchenne/Becker muscular dystrophy, fragile X chromosome syndrome, haemophilia and other disorders)

PGS – step by step

1. IVF/ICSI manipulation
2. Cultivation of the received embryos up to day 5
3. Embryo biopsy – several trophectoderm cell collection without harming the embryo
4. Embryo freezing (vitrification) for later use
5. PGT-A/PGS – Preimplantation Genetic Testing – Chromosomal analysis
6. Selection of genetically competent embryos for embryo transfer
7. Embryo transfer