Preimplantation Genetic Screening (PGS) and Preimplantation Genetic Diagnosis (PGD) are types of Preimplantation Genetic Testing performed before embryo transfer during IVF. Although the tests are used for different things, the goal for both is to improve your chances of choosing a healthy embryo, and therefore, a healthy baby.
As you progress through your infertility journey, you begin to hear more and more of what seems like alphabet soup. If you have been recommended by your fertility specialist to do IVF (In Vitro Fertilization), you may have been recommended to add a PGS or PGD testing as well.
When it comes to PGS and PGD testing, we have realized that Intended Parents tend to have similar questions:
“So, what exactly is PGS or PGD?”
“Is it necessary?”
“Will it increase our chances of success?”
We hope you will find the information on this page helpful. As always, if you have more detailed questions about your specific situation, feel free to contact us.
PGS stands for Preimplantation Genetic Screening. The main purpose of a PGS test is to screen embryos for potential chromosomal abnormalities. PGS test determines if there are the correct number of chromosomes in each embryo and allows for a healthy implantation and pregnancy.
PGD stands for Preimplantation Genetic Diagnosis. This test is useful for intended parent(s) who wish to screen their embryos for a specific genetic condition, like Tay-Sachs, Sickle Cell Anemia, Cystic Fibrosis, among many others. Generally, PGD testing is recommended for individuals with a family history of disease and individuals who are concerned that they may be carriers of genetic disease. PGD testing is 98% accurate in identifying affected and unaffected embryos for approximately 2,000 inherited single gene disorders.
Your fertility specialist will let you know which of these two is recommended based on your individual needs.
PGS and PGD are tested in similar ways. After the IVF process takes place and the embryos are grown to approximately day 5 blastocysts, a small number of cells is retrieved from each embryo and sent to a laboratory for testing. The embryos are then frozen at this stage while we wait for the genetic testing results.
Everyone can benefit from genetically testing their embryos. Genetic testing increases the success rate and ensures that you are transferring an embryo that is genetically normal. Genetic testing also reveals the gender of the embryo so is beneficial for patients who are seeking family balancing through gender selection.
The results from PGS and PGD testing can take anywhere from 12 hours to a month, depending on the laboratory. The report is sent to your fertility specialist who will then counsel you on which embryos are genetically normal and will result in the best possible pregnancy outcomes.
As women age, the percentage of eggs with chromosomal abnormalities increases. Preimplantation Genetic Screening (PGS) is performed to test embryos for these abnormalities before an embryo transfer. The number one failure of IVF is chromosomal abnormalities of the transferred embryos which frequently results in miscarriage. By performing PGS, we are able to ensure the embryos are genetically normal prior to transfer, thus, greatly reducing the chance for miscarriage during the first trimester.
Using PGS or PGD can increase the likelihood of a successful pregnancy and decrease the chances of a genetic disease. Prenatal diagnostic testing can help confirm the results of PGS or PGD after conception has occurred.
Embryos created via IVF are grown for 5 days to the blastocyst stage where they undergo several hundreds of thousands of divisions. A small sample of tissue is taken from the ever-growing embryo, and is sent off to a genetics laboratory for PGS testing. The laboratory scans thousands of DNA sequences to identify any missing or extra chromosomes. Once the testing is complete, a report is sent to your fertility specialist who will be able to make more informed decisions about which embryos should be transferred, giving you the best chances for a successful pregnancy. Some clinics are now offering fresh Day 6 transfers of PGS tested embryos whereas other clinics freeze all Day 5 blastocyst embryos and require the Intended Parent to have a frozen embryo transfer. You should inquire with your fertility clinic if they offer fresh embryo transfers with PGS.
A 2005 study published in the Acta Obstetricia et Gynecologia Scandinavica found that 61% of first-trimester miscarriages were caused by chromosomal abnormalities. 37% of these abnormalities were autosomal trisomies, which is where a non-sex chromosome pair has an extra chromosome. A common example of this condition is called trisomy 21 which causes Down syndrome. 9% of the abnormalities were polyploidies (having multiple chromosomes) and 6% were found to be monosomy X (having a single X chromosome).
PGS is able to detect chromosomal abnormalities so intended parents know which embryos are healthy for transfer. And if gender selection is your goal, sex chromosomes are also identified through PGS, so you can also know what sex each embryo has before the transfer.
While women over age 35 are at higher risk of chromosomal abnormalities in their eggs, a genetics laboratory found that approximately 36% embryos conceived from donor eggs (from women less than age 30) have a genetic abnormality (versus 45% at age 35).
85% of Donor Nexus’ intended parents in 2018 chose to have PGS performed on their egg-donor-conceived embryos to increase their chances for first-time transfer success.
Now that we have briefly described how Preimplantation Genetic Tests may benefit your egg donor cycle, we encourage you to talk to your fertility specialist about whether PGS/PGD testing is right for you. If you have any questions, our team will be happy to assist you.