Preimplantation Genetic Diagnosis, also referred to as PGD testing, is a group of genetic assays used along with IVF to check your embryos for genetic defects, before implanting them in your uterus. This helps prevent the genetic disorders from being passed to the next generation.
Using this “embryo biopsy” technique, the embryologist can test the embryos for abnormalities in chromosomes as well as hereditary conditions. PGD is helpful for patients who are carriers of chromosomal or genetic disorders and fear passing them on to their children.
Although initially there were some concerns regarding the use of this technology, but it has been proven safe over trials and uses of many years and is widely used with IVF cycles today.
Kinds of genetic testing
Major health societies such as ASRM, ESHRE, and ICMART collectively decided to rename genetic testing procedures, so the terminology better represents what they actually stand for:
Pre-implantation genetic diagnosis (PGD) is now referred to as:
- Preimplantation genetic testing-monogenic (known as PGT-M): to detect single gene disorders
- Preimplantation genetic testing-structural rearrangements (known as PGT-SR): to check for structural chromosomal abnormalities, such as translocations
PGD looks for specific genetic disorders or inherited chromosomal rearrangements, and these two techniques are applicable for different kinds of patients and employ different technology platforms.
For the purpose of this article, we will use PGD collectively for the two genetic testing techniques: PGT-M and PGT-SR.
What is the difference between PGD and PGS?
Unlike PGD, Preimplantation genetic screening (PGS) does not check the DNA or identify a specific genetic disease. It is simply used to check the embryos for aneuploidy (abnormal numbers of chromosomes), which is the main cause of miscarriage and implantation failure, causing frustration to a lot of IVF patients.
Under the new nomenclature, PGS is now known as Preimplantation Genetic Testing for Aneuploidies (PGT-A).
Disorders like Down’s syndrome—caused by the presence of an extra chromosome 21—can be avoided with PGS.
Using PGS the doctor can simply identify the embryos that have too many or too few chromosomes, so those can be left behind and only the normal ones are transferred, thus raising the possibility of successful pregnancy.
Read more about the uses and benefits of PGS.
PGD on the other hand is significantly more complex as it examines the genes that make up the chromosomes and checks them for specific diseases. So, if there is any indication of you or your partner having any history of genetic diseases, you will likely need PGD.
How is PGD performed?
First, the intending parents are assessed for the genetic problems that can possibly be transferred to the offspring. You need to have a detailed genetic report so the laboratory knows which genetic problems are they looking for, in the embryo.
Once established, the normal process of in vitro fertilization will be carried out, during which the egg and sperm are fertilized in the lab. The resultant embryo will divide into multiple cells in the next three to five days.
Steps of the PGD procedure:
- Biopsy: The embryologist will take a very small sample of several cells from the embryo on the 5th day of its growth. The day-5 biopsy on blastocyst is considered by many experts to be the gold standard for PGD testing.
- DNA evaluation: While the embryos remain frozen in the lab, the DNA of extracted cells is evaluated to check for presence of any problematic gene.
- Embryo Selection: The embryos that pass as problem-free will be transferred to the uterus and if there are still other good ones left, they will be kept frozen for future use.
In the below video, Dr. Lam Wei Kian from one of Asia-Australia’s top genetic testing and fertility clinics, explains how PGD testing is performed:
How much time is required for PGD?
If you opt for PGD testing with IVF, you will have to wait 2-3 weeks extra to allow for the screening of embryos before implantation.
In some clinics, you can also have PGD done on fresh embryos (day 3) and have the embryos implanted on day 5. However, PGD testing on day 3 embryos can be harmful for them and it may also not show accurate results because the cells have not completely developed by that stage.
PGD testing on day 5 of embryo development (blastocyst stage) and transfer of frozen embryos is recommended for best results. If you are going abroad for IVF-PGD, it is best to plan two trips (one for egg pickup and the other for embryo transfer), or one long trip of 7-8 weeks.
Even without genetic testing, many doctors prefer to do transfer of frozen embryos vs. fresh in IVF, as they believe the results are better once the woman’s body has rehabilitated to its normal state after the stimulation program.
Do you need PGD testing with IVF?
PGD may be helpful if you can identify with any of the following situations:
- You have family history of sex-linked genetic diseases
- You are a carrier of single gene disorder
- You have a previous child with a genetic problem
- You or your partner is a carrier of chromosomal translocations
- You have had recurrent miscarriages
- You have suffered repeated IVF failure
With PGD your doctor can identify translocations in chromosomes (rearrangements of parts of chromosomes) as well as single mutations in genes that can cause genetic diseases.
PGD can effectively identify embryos for genetic disorders such as Tay-Sachs disease, cystic fibrosis, sickle cell anemia, muscular dystrophy, fragile X, thalassemia, and about 4,000-single gene disorders.
It is also helpful to raise your chances of success if you are seeking IVF in advanced age —after 36 years, as there is a greater chance of chromosomal anomalies in female eggs as they get older.
Look at the below chart from the New England Journal of Medicine
If there is no reason to suspect genetic problems and you are only getting genetic testing to improve your chances of success in IVF, you may undergo PGS instead of PGD.
Read all about the indications for PGD testing, and whether it is right in your situation.
Cost of PGD
The cost of PGD testing is determined by the number of embryos and the disease or anomaly we are checking for. How well equipped your testing lab is and the location of the fertility clinic are two other factors that determine the cost of PGD.
We offer IVF-PGD or pre-implantation genetic testing at some of the top fertility centers in Thailand, Malaysia, India, Ukraine, Mexico, Denmark, and Cyprus.
Benefits of PGD testing
The main reason to use PGD is to lower the chances of passing genetic diseases to your children. PGD can help to:
- Identify embryos that carry one or more genetic disease and conditions.
- Check the embryos for potential problems in the embryo to let you decide if you want to continue with the pregnancy.
- Allow carriers of genetic disorders to safely plan a pregnancy with a significantly lower risk of passing those disorders on to their children.
- Improve the chances of a healthy pregnancy by selecting the healthiest, best quality embryos for transferring to the uterus.
Limitations and Risks of PGD Testing
- Extra time needed before embryo implantation
- If the results are not recorded carefully, an embryo with a chromosomal defect could be transferred to the uterus and healthy embryos are discarded
- Not all genetic diseases can be detected—it is not a comprehensive test and cannot not screen for all possible genetic problems. Disease like the ones that begin to show only when the carrier reaches middle age may also not be detected. PGD greatly improves the chances of conceiving a child without a genetic disorder but it does not completely eliminate the risk
- If considering PGD, you must also be prepared for the possibility that all the embryos tested may come out as genetically inadequate, meaning that none would be good to transfer. In this situation, the doctors will share the other possible options and you may be asked to consider IVF with donor eggs or donor sperm
Is PGD testing safe?
Some people believe that taking cells for a biopsy so early on could disturb the embryo but data from years of PGD tests reveals that these tests do not raise the risk of birth defects in a new born.
Embryos are delicate and PGD is quite a sophisticated procedure, so there is some measure of risk if the process not handled carefully. Infertility Aide only works with the doctors and genetic laboratories that have extensive experience and have been using these technologies successfully for years.
It is rather unsafe to carry on IVF without PGD (in cases where it is especially indicated) and risk a miscarriage or carry a baby with a serious genetic disorder to birth.
Alternatives to PGD testing
Preimplantation genetic testing is done on embryos before they are transferred to the uterus. There are also some tests that can check for genetic abnormalities, AFTER the pregnancy is confirmed. These include:
- Chorionic villus sampling (CVS) – biopsy of the placenta at 10 -12 weeks of pregnancy to detect for fetal genetic abnormalities. If detected, you may have to consider an abortion.
- Amniocentesis – performed 16 to 18 of pregnancy. In this test the amniotic fluid is checked for genetic abnormality in the fetus.
- Ultrasound & blood tests – additionally help in checking for some abnormalities. If suspected, advanced tests may be recommended to confirm the diagnosis.
For more information and to know about the cost of IVF with PGD testing in your specific situation, get in touch via the form on this page.
With contributions from Dr. Lam Wei Kian, IVF expert.
Resources:
Human Reproduction Open, Volume 2020, Issue 4, 2020, hoaa043, https://doi.org/10.1093/hropen/hoaa043
A.R. Thornhill, C.E. deDie-Smulders, J.P. Geraedts, J.C. Harper, G.L. Harton, S.A. Lavery, C. Moutou, M.D. Robinson, A.G. Schmutzler, P.N. Scriven, K.D. Sermon, L. Wilton, ESHRE PGD Consortium ‘Best practice guidelines for clinical preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)’, Human Reproduction, Volume 20, Issue 1, January 2005, Pages 35–48, https://doi.org/10.1093/humrep/deh579