Preimplantation Genetic Screening (PGS)

Preimplantation Genetic Screening (PGS)

Preimplantation Genetic Screening (PGS)

PGS involves checking the chromosomal constitution of embryos following IVF or ICSI, for common abnormalities, before transferring them to the uterus.

Chromosomal abnormalities are a major cause of failure of embryos to implant and of miscarriages. Normal healthy human embryos have 23 pairs of chromosomes. In cases of chromosomal abnormalities there may be excess or less number of chromosomes than normal. PGS enables detecting such abnormalities that may be present in the genes.

PGS is advised for couples where a woman’s age is more than 35 years as they have a higher risk of having a baby with chromosomal abnormalities, in cases of history of chromosomal problems or recurrent miscarriages, or if a couple had undergone several unsuccessful IVF cycles.

 Steps involved in PGS

  • An IVF/ICSI treatment to collect and fertilize eggs
  • The embryos grow in the lab for a duration of 5 days or until a blastocyst is formed
  • A trained embryologist removes one or two cells from the blastocyst stage of embryos
  • The embryologist then examines these cells for checking the chromosomal constitution to see how many embryos are normal.
  • The healthy embryo is transferred to the womb and is then allowed to develop

Besides, it is also possible to remove cells/ blastomeres from day 2/ day 3 embryos; however, PGS done with blastocyst stage leads to more accurate results.

There are some risks that come along with the use of PGS; Embryos are very fragile due to which the procedure of cell removal may damage the embryos; there may not be any normal embryo leading to no embryo available for transfer, screening of embryos has accuracy of approximately 95-96% so there is still a small risk of miscarriage after PGS.

At the same time, PGS has many advantages. The implantation of most viable embryos can help improve implantation rates, reduce spontaneous abortion and enable single embryo transfers, thereby decreasing the risk of multiple pregnancies.

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