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:
- If the patient is over 35 years of age and have a higher risk of having a baby with a chromosome problem (such as Down’s syndrome).
- Having genetic history of chromosome problems.
- History of recurrent miscarriages/abortions.
- Patient has undergone several unsuccessful cycles of IVF where good embryos have been transferred.
- Also if sperms are known to be at high risk of having chromosome problems.
However, various studies have questioned whether or not PGS is really effective at increasing the chances of a live birth.
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.
Some centers may test eggs for chromosomal abnormalities before they are used to create embryos. Polar bodies (small cells extruded by eggs while they mature) can be extracted and tested.
Comparative Genomic Hybridization (CGH), Few clinics are now using a procedure called comparative genomic hybridization (CGH) which allows them to test for abnormalities in all 23 chromosomes.
These abnormalities may or may not be of great biological significance, but their presence will lower the chance of finding any suitable embryos for transfer.
Some of the risks in PGS treatment are similar to those for conventional IVF.
Risks of PGS in fertility treatment:
Other problems unique to PGS procedure include:
- Some embryos may be damaged during the process of cell removal.
- Possible that no embryos are suitable for transfer after PGS.
- It is important to understand that there is no guarantee against a miscarriage/abortion occurring even though PGS has been carried out prior to embryo transfer.
It can be performed for a patient at high risk of carrying an inheritable genetic disease. Using this technique, embryos that do not carry the disease can be selected for transfer.
PGD (Preimplantation) Genetic Diagnosis):
We carry out PGD procedure in collaboration with IVIOMICS. The whole PGD procedure for testing is done by specialist team of IVIOMICS (from Spain) in their specialized laboratory.
PGD involves extracting a cell from the IVF embryo and tests it for some specific genetic condition or disorder like cystic fibrosis. Once it’s examined and identified to be safe, it’s transferred to the child.
What is PGD?
PGD procedure or Preimplantation Genetic Diagnosis is a latest technique, which combines the recent spectacular advances in molecular genetics and assisted reproductive technology (ART). Before the establishment of pregnancy, it enables the doctors to identify genetic diseases in the embryo prior to implantation.
It enables people with an inheritable condition in their family to avoid passing it on to their children. It involves testing the genes of embryos created through IVF.
In-Vitro Fertilization (IVF), because it is being done outside the body and has the advantage to undergo a testing to identify genetic defects in embryos. Amniocentesis or Chorionic villus sampling done to diagnose genetic defects are carried out during pregnancy, in case of test resulting positive, a very difficult step like termination of pregnancy is the only option to go for.
But, Preimplantation Genetic Diagnosis PGD/PGS has empowered the doctors to save the couple from getting into such problems.
Is PGD treatment for you?
Your doctor may recommend PGD treatment to you if:
- You have ended previous pregnancies because of a serious genetic condition.
- You already have a child with a serious genetic condition.
- You have a family history of a serious genetic condition.
- You have a genetic issue of chromosome problems.
Which Genetic Conditions can be tested During PGD Treatment?
PGD procedure can be used to test for virtually any genetic condition, where a specific single gene is known to cause that condition. It is currently approved for over 250 genetic conditions.
Some common conditions where it is recommended are:
- Cystic Fibrosis
- Sickle Cell Disease
- Spinal Muscular Atrophy
- Huntington’s Disease
Preimplantation Genetic Diagnosis (PGD treatment) can also be called as a technique that enables people with a specific inherited condition in their family to avoid passing it on to their children. It involves checking the genes of embryos developed through IVF for a particular genetic condition.
What are the risks of PGD Treatment?
Most of the risks involved in PGD treatment process are similar to those for conventional IVF.
- Some embryos could be damaged during cell removal.
- Testing may not be 100% reliable.
How Does PGD works?
The procedure for PGD procedure is normally as follows:
Step 1: You undergo normal in vitro fertilization (IVF) process to collect and fertilize your eggs.
Step 2: The embryo is grown in the lab for few (two to three) days until the cells have divided and the embryo consists of approx. eight cells.
Step 3: A specialized embryologist removes one or two of the cells (blastomeres) from the embryo.
Step 4: The cells are tested in detail to see if the embryo from which they were removed contains the gene that causes that genetic condition in the family.
Step 5: The embryo unaffected by the condition is transferred to the womb and allowed to grow.
Step 6: Any suitable remaining unaffected embryos can be frozen/cryopreserved for later use. Those embryos that are affected by the condition are allowed to perish or with the patient’s consent, used for research.
The short coming for this test is also the same as for PGS.
Both PGS and PGD involve testing embryo cells. They both detect genetic irregularities in embryos prior to embryo transfer and thereby offer better success rates.
IVF success rates with PGS/PGD:
PGS and PGD are both advanced technologies in assisted reproduction and both help to improve success rates in IVF procedure. While PGS is used to eliminate aneuploidy (abnormal chromosome numbers); PGD helps eliminate genetic disorders. All good IVF clinics these days have embryo culture and vitrification technology in place to improve success rates. Both these technologies along with PGS and PGD are great help to improve IVF success rates. PGS/PGD may not be necessary in most cases but in repeated IVF failure cases it helps to find healthy embryos for implantation.