What is PGS/PGD?
PGS, (preimplantation genetic screening), stands for testing of overall
chromosomal normalcy in IVF embryos. It involves taking embryo biopsy from
an IVF embryo and screen for normal number of chromosomes before embryo transfer.
PGD (preimplantation genetic diagnosis), involves removing a
cell from an IVF embryo to rule out a specific genetic condition,
to exclude a particular genetic condition, before transferring the embryo to the uterus.
These tests are performed by a genetic laboratory.
These tests are performed at our centre in collaboration with Iviomics (Spanish company).
Embryo biopsy is done to diagnose embryo quality for chromosomal
or genetic abnormality. It is generally performed for patients at high risk
of inheriting a chromosomal disorder or a genetic disease. By using this technique we
can avoid transferring genetically abnormal embryos.
PGS (also called aneuploidy screening) involves checking the
chromosomes of the embryos conceived by IVF/ICSI for common abnormalities.
Chromosomal abnormalities are a major cause of the failure of embryos to implant
and of miscarriages/abortions. They can also cause conditions like Down’s syndrome.
Most of the patients are confused for the condition in which PGS is best for you.
Before any decision about genetic testing is taken, we review each couples history
/family history and offer the best possible option to them. But generally your doctor
may recommend PGS if:
Steps for the PGS procedure:
Step 1: You undergo a normal IVF/ICSI treatment to collect and fertilize your eggs.
Step 2: The embryo is grown in the lab for two to three days till the cells have divided and the embryo consists of around eight cells.
Step 3: A specialized embryologist removes one or two of the cells (blastomeres) from the embryo for testing.
Step 4: The chromosomes are examined to see how many there are and whether they are normal or not
Step 5: One/two/three of the embryos without abnormal numbers of chromosomes are transferred to the womb so that they can develop.
And if any embryos are left they can be frozen for later use.
Step 6: The embryos with abnormal chromosomes are allowed to perish or may be used for research (with the patient’s consent).
Step 7: Testing at day 5 or 6: It is possible that instead of
removing and testing one or two cells from a day two or day three old embryo, some centers may allow the embryo to develop
up to day 5 or 6, when there are approximately 100-150 cells.
More cells may be removed at this stage without compromising the viability of the embryo, possibly leading to a more accurate test.