PGS & PGD
Preimplantation genetic diagnosis or PGD is a test to screen the single cells from an embryo for genetic or chromosomal disorders. This testing is a part of the IVF procedure and is done prior to the embryo transfer. PGD allows those with an inheritable condition in their family to avoid passing it on to their children. It involves checking the genes and/or chromosomes of embryos created through IVF.
Preimplantation genetic screening or PGS is for those who have experienced recurrent miscarriages. PGS takes notes from PGD to help enhance the chances of pregnancy. Here, the embryos are screened for aneuploidy, i.e. the number of chromosomes that is either missing or additional. The reason why PGS is conducted is that the leading cause of miscarriage and implantation failure is aneuploidy.
So, basically, PGS involves checking the chromosomes of embryos conceived by IVF or ICSI for common abnormalities. Chromosomal abnormalities are a major cause of the failure of embryos to implant, and of miscarriages. They can also cause conditions such as Down’s syndrome.
PGD can be used to test for virtually any genetic condition where a specific gene is known to cause that condition.
A study conducted by the Mastenbroek and Colleagues, they examined about 408 women who were undergoing IVF treatments at Dutch centers. This was done during a period from May 2003 to November 2005. So, then they divided 206 women to get the genetic screening done and the remaining 202 did not go for any testing or screening. However, the results showed that the first group experienced 24% success and the second group with no testing experienced 37% success. But, the results were so because the testing took place on the third day. Nevertheless, today to avoid immature testing, the specialists do the testing on the 5th day.
Why is it performed?
As mentioned earlier, PGD and PGS is a reproductive technology, which helps identify and prevent any genetic disorder from the embryo.
Benefits of PGS and PGD
PGD and PGS is exceptionally beneficial for;
- Patients who have repeated IVF failures
- Patients who had a history of recurrent miscarriages
- Patients who have ended previous pregnancies because of a serious genetic condition
- Patients who already have a child with a serious genetic condition
- Patients who are the carriers of abnormal chromosomes or have a family history of serious genetic disorders or chromosomal problems.
- Patients who are 38 years and above who are undergoing IVF cycles
These tests may help identify the problems that are causing infertility. Once diagnosed, the problems can be treated by our doctors.
It can help identify;
- Incorrect number of chromosomes, which can cause downs syndrome or Edwards syndrome
- It can identify the rearrangement of a part of the chromosome onto another chromosome.
- It can see if a chromosome is missing
- It can determine if the sex chromosome includes any duplicates or any deletion of the x and y chromosome. This can prevent Klinefelter Syndrome and Turner Syndrome.
How is it performed?
After the embryos are created in the laboratory, they are left alone for 4-5 days in order for them to mature. On either the day five or the day six, the biopsy is performed for PGD. During the biopsy, a few cells are removed from the trophectoderm, i.e. the layers of cells that are hatching out of the embryo as a process for development and will form the placenta. The embryos are safely stored and the genetic material present inside the cells are extracted to test them for any abnormalities. Finally, once the results are out, the specialist will talk to the couple to let them know about the results.
It is a very intricate procedure, which can be carried out only by skilled embryologists. The embryos that are affected by some genetic disorders are either allowed to perish or can be donated by the couple for research and testing.
Like any treatment, PGS and PGD to come with their portion of risks. They are;
- To undergo PGS and PGD you will first have to opt for IVF, therefore, the risk of ovarian hyperstimulation syndrome increase & multiple pregnancies increases.
- Complication can occur during biopsy and freezing of the embryo
- If there is a glitch in the results, it could mean the defective embryo gets transferred into the uterus. And, this can result in miscarriage, and since the healthy embryos (remaining ones) gets destroyed, your chances of experiencing a healthy pregnancy also decreases.
- The test can also reveal that the patient has no healthy embryos in her system.
NOTE: These tests cannot completely guarantee to find all the genetic disorders. So, if you undergo these tests, it is not a given the baby will be fully healthy.
Possible results from PGS and PGD analysis of embryos
- Normal Embryo – It shows the exact number of chromosomes and is suitable for transfer.
- Abnormal Embryo – The number of chromosomes is less, and the chromosomes have been deleted. Hence, it is not fit for transfer.
- Partial deletions – Here, a small amount of genetic information is missing from maybe a single or more chromosomes. However, there is no complete loss of chromosome. Some embryos may be eligible for a transfer, but the pregnancy chances become low.
- Mosaic – The analyzed cells are a bunch of normal and abnormal cells. Some may be suitable for transfer, but it decreases the chances of pregnancy.
- No Result – The biopsied cells were not in a condition to be analyzed and this happens in extremely rare cases.
Q. Is PGD safe?
A. If you start counting, thousands of PGD and PGS testing are done all across the world. And, this has resulted in the births of thousands of healthy babies. This technology came into existence during the 1990s and has been getting the update, to stay useful. Yes, this procedure is safe when a highly qualified embryologist or specialist conducts it. It does not affect the embryo development or the baby.
Q. When is embryo biopsied?
A. Usually, the embryos were biopsied on day 3 of the embryo development. But, during this stage, the embryo contains only 6-8 cells. However, today it is biopsied during the blastocyst stage. This is because they have about 200 cells or more.
Q. Should I again get tested during pregnancy?
A. PGS is not a replica of prenatal testing. Therefore, it is important to repeat the testing during pregnancy.
Q. Can PGD and PGS be performed together?
Q. How are the embryos chosen for transfer?
A. Embryos that come back with positive results after the testing are transferred to the frozen embryo transfer (FET) cycle. Usually, you need embryo with morphology. But, even the embryos with abnormalities can have decent morphology. Therefore, with the help of PGD results, the best embryo is chosen for transfer.
Q. How much does it cost?
A. It starts from INR 20,000/embryo.
Q. Where does the PGD testing take place?
A. It is always performed in a laboratory.
Q. Will there be any embryo loss?
A. The biopsy can damage the embryos, or they might expire after the procedure. Therefore, if the embryo count is less, it is better to skip the step.
Q. Can I know the sex of the baby through PGD?
A. Although it is possible, it goes against the ethics of the clinic, therefore, the doctors will not promote the same.
Q. Does it screen chromosomes?
A. Yes, all 23 pairs.
Q. How often is the test conducted during pregnancy?
Q. What are the pros and cons of this testing?
A. When you select to transfer the chromosomally euploid embryo, i.e. having the correct set of chromosomes, the success rates go up higher with each transfer. And, the reason is the chosen embryos are healthy and you are not dealing with any abnormal ones.
One of the cons is that the embryos must grow into the blastocyst stage for the specialist to completely analyze the cell. And, this is a disadvantage because normal embryos might not make it to the blastocyst stage. Therefore, if the patient is an older woman or with advanced maternal age, her embryos are already minimal. Hence, it is risky to take a chance until the embryo reaches the desired stage.
Q. What is the difference between PGD and PGS?
A. PGD is where the embryo is tested for a specific condition, such as cystic fibroids, etc. In PGS, the overall chromosomes are tested to identify any genetic misdemeanor. It is done to ensure a healthy embryo is being transferred inside the uterus.