When one is planning for an IVF treatment, it is very important to get Genetic Testing completed. The trying couples may have some medical conditions that would affect their children later. Not to mention, they may pass on their condition to their offspring, as some disorders are hereditary in nature. And IVF treatment is performed when regular conception is not working. Thus, Genetic Testing would also ensure that one has a safe pregnancy through IVF.
Therefore, Preimplantation Genetic Testing is an important step to do before the embryo is moved into the uterus. Through his diagnostic process, doctors screen the embryos and see if they are in healthy conditions. There are two particular types of embryo testing that fall under this. They are PGD and PGS, and both of them have their advantages. However, there are some distinctions between both. When doctors check for the genetic condition of the embryos, the style of diagnosis works for different types of cases. To understand these differences, it is important to under both genetic testing styles.
What is PGD?
The term PGD stands for Preimplantation Genetic Diagnosis and is a very important type of genetic testing. In this, the main aim is to see if the embryos contain any chromosomal or genetic disorders. Embryologists screen cells singularly in the embryos for this alongside regular IVF (in-vitro fertilization) treatment.
While this is done while the IVF is occurring, the screening process happens right before the transfer of the embryos. This is an important step to undergo before the pregnancy can take effect. In this, the couple who is getting the test can notice and choose the embryos that would form into a successful pregnancy.
With PGD, the main goal is to notice any abnormalities in the chromosomal and genetic makeup of the cells. Thereafter, they can choose completely disease-free embryos and that would support the growth of babies without any future defects. Owing to this process, experts can notice any rearrangements in the chromosome segments. This is known as chromosomal dislocations. Also, they can see if any of the mutated genes have given rise to genetic diseases. This condition is called single-gene disorders and, in total, there are more than 4,000 different types of it.
There are some very common disorders that the doctors check for using the PGD format. A few of them are Thalassemia, Cystic Fibrosis, Fragile X, Tay Sachs, and Myotonic Dystrophy.
Moreover, another interesting development that parents would appreciate about this is checking the gender. This technology can showcase what the embryo composition is; XX chromosome (girl) or XY chromosome (boy). Due to this, some prospective parents can also select a particular gender that they want for their baby. If there are more than one viable embryos and they have different sexes, the doctors can implant the preferred type.
PGD is not suitable for every type of person, but those who have a certain genetic predisposition. Plus, if they are more likely to pass a genetic disorder they know they have, PGD is suitable for them. For example, if a couple has a history of some disorders like aneuploidy in their family, they should have PGD testing. The common conditions that they would face because of this are birth defects, miscarriages, and Down Syndrome.
Moreover, in some families, many single-gene defects are visible down their bloodline. Some of the common disorders are muscular dystrophy, sickle cell anemia, and cystic fibrosis. Thus, if the trying couple has seen these in their family history, the doctor would suggest PGD testing. They check to see which embryos are in good condition and prepare them for the transfer into the female’s uterus.
What is PGS?
Some couples tend to undergo a lot of pregnancy losses each time they try. If one person in the couple has infertility problems, they have a similar recurring problem when trying to conceive. Here, PGS or Preimplantation Genetic Screening is the best testing method to go forward with.
The screening system of this works similar to that of the PGD testing style. And the outcome of this screening makes it easier for the couple to get pregnant later. Aneuploidy, as mentioned earlier, is a condition that results in such pregnancy failures. In this, there is an abnormal count in the chromosomes, either too many than normal or too less.
If a person has this issue, the embryologists screen their embryos to see which are defective. The defects generally result in them not implanting into the uterine line properly and often lead to miscarriage.
The goal of this process is similar to that of the PGD type of genetic testing. Doctors study the embryos that are chromosomally abnormal and leave them out. They select the normal embryos instead and use them in the IVF treatment process for successful fertilization.
There are some particular types of people who benefit from this type of genetic testing. Doctors suggest this type of screening for those couples who want to pursue the transfer plan for a single embryo birth. Also, if some of the couples have tried the IVF treatments before without success, they can utilize this.
Some women have a volatile uterus or other conditions that lead to miscarriages continuously. Doctors would recommend this testing plan for them. Plus, a few people may desire a particular type of gender for their baby. They, too, can benefit from PGS diagnosis. Not to mention, women in the later years of their lives have more complications than younger women. Thus, those who are over 38 years of age but want to try for a child can opt for this screening method as well.
The procedure of Embryo Testing
The embryo testing procedure for both these testing styles needs a biopsy first. The doctors do so on the cells of the blastocyst embryo, and the procedure is specified as embryo biopsy. This occurs in the embryology labs, and the embryos are screened under a controlled laboratory environment. Many of the embryos do survive after the biopsy is over but some do not. Statistically speaking, the embryos that are biopsied do not show a bigger risk for birth defects in comparison to non-biopsied embryos.
After this, they reach the testing lab where the embryologists store the remaining embryos for future use. Then, they wait for the results and patients can also choose what to do with the frozen embryos. After the results appear, patients alongside their doctors prepare a plan for the future insemination. They select an embryo, specifically those without chromosomal defects for transfer.
Which is better for you between PGD and PGS?
There are many ways in which couples would benefit from the use of gene testing through both PGD and PGS formats. However, you should know which is better for you depending on your circumstances. As mentioned earlier, someone who had particular genetic disorders would get a more accurate result with PGD.
Yet, if the main reason for the need for testing is because of a history of failed IVF treatments, PGD would not work here. Plus, if a woman is over the age of 38 they would get a better analysis using PGS. This is because it screens the embryos without focusing on diseases, unlike PGD. It is important to consult with your specialist to see which is more fitting, based on your circumstance and medical history.
Dr. Jay Mehta
Fertility and IVF Specialist
Dr. Jay Mehta is the Scientific Director of Shree IVF Clinic. He is a well-known Fertility and IVF Specialist and also among few doctors in the country who specializes in Embryology and Andrology.