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A significant portion of embryos created naturally, up to 70%, are of low quality. Many embryos also fail to successfully implant in the uterus due to abnormalities or certain genetic disorders after IVF. Therefore, these embryos cannot complete the early months of pregnancy healthily, and the pregnancy ends. In this article, we answer common questions about IVF genetic tests.
Preimplantation genetic testing (embryo biopsy) directly targets these statistics and is one of the most important discoveries in reproductive medicine.
What Do Genetic Tests Do?
Through preimplantation genetic tests performed during the IVF cycle, our doctors and laboratory team can identify genetic defects or chromosomal abnormalities in an embryo.
As a result of this test, high-quality embryos that are chromosomally normal are selected. The selected embryos have the best chance of implantation in the uterus and subsequent healthy fetal development.
At our clinic, two types of genetic tests are offered for embryo evaluation: preimplantation genetic screening (PGT-A) and preimplantation genetic diagnosis (PGT-M) tests.
The previous names for these tests were preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) tests.
- With PGT-A, we identify the cause of repeated pregnancy losses or failed fertility cycles. We select the best embryos before implantation. This way, we increase your IVF success rate.
- With PGT-M, we determine whether you and your partner are at risk of having a child with a specific genetic disease, and we eliminate the possibility of passing it on to your children.
- Both PGT-A and PGT-M tests can be applied in the same embryo biopsy. This increases the chance of healthy live births.
What is PGT-A (PGS) Test?
The ‘chromosomal structure’ is one of the important factors for a successful pregnancy.
As women age, a significant portion of their embryos become genetically abnormal.
This high proportion of genetically abnormal embryos (aneuploidy) is a factor that increases the likelihood of failed IVF cycles and repeated miscarriages in older women.
Aneuploidy is more common in older women, but all pregnancies carry a risk of chromosomal abnormalities.
Preimplantation genetic testing for aneuploidy (PGT-A) involves transferring embryos without significant chromosomal abnormalities. This increases pregnancy success and healthy baby births. PGT-A was previously known as PGS (preimplantation genetic screening).
What is PGT-A?
In this test, one or more cells are taken from embryos before transfer during IVF and genetically analyzed in our laboratory. If the chromosome count in the cells is abnormal, the embryo has a lower chance of successful implantation in the uterus.
PGT-A is a laboratory test that helps identify embryos with normal chromosomes. It frequently uncovers chromosomal abnormalities that lead to failed fertility cycles and miscarriages.
PGT-A allows us to scan and select the most suitable embryos for embryo transfer. As a result, fertility success rates increase, and miscarriage rates decrease. PGT-A improves the success rates of IVF cycles.
Who Should Undergo the PGT-A Genetic Test?
- Women with age-related infertility
- Women who have undergone failed cycles
- Women with unexplained IVF failure
- Women who have experienced multiple miscarriages
- Male factor infertility
What are the Benefits of PGT-A?
- Increases fertility success rates,
- Reduces miscarriage rates,
- Decreases the risk of failed IVF cycles,
- Facilitates the identification of embryos with normal chromosomes,
- Increases the chance of successful embryo implantation,
- Reduces the need for multiple IVF cycles,
- Identifies significant chromosomal abnormalities with 98% accuracy.
Things You Should Know About PGT-A / PGS Genetic Test:
- About 50% of miscarriages are caused by chromosomal abnormalities.
- In miscarriage cases, 68% of embryos are chromosomally abnormal. Chromosomally normal embryos have a higher chance of live birth.
- Some chromosomal abnormalities prevent the embryo from implanting in the uterus.
- Embryos with normal chromosomes have a higher chance of successful implantation.
- Male factor infertility (including abnormal sperm count and quality) increases the risk of chromosomal abnormalities in embryos.
- PGT-A can be used to detect Down syndrome.
- If you decide to add PGT-A to your treatment plan, you can consult your doctor about any additional costs.
PGT-A and Advanced Age
As a woman’s age increases, the risk of chromosomal abnormalities and genetic anomalies rises. This reduces the likelihood of pregnancy and increases the risk of miscarriage. Abnormal embryos that result in pregnancy can lead to miscarriage or a baby with chromosomal abnormalities.
If you are nearing 40, have had multiple miscarriages, or have undergone several failed IVF cycles, we recommend undergoing PGT-A to determine whether your embryos are healthy before implantation.
Does PGT-A Reduce Miscarriage?
Yes. In IVF cycles without PGT-A, embryos are primarily selected based on visual characteristics. In this way, chromosomally normal and abnormal embryos cannot be distinguished.
In IVF cycles with PGT-A, it is possible to identify embryos with normal chromosomes that will result in a healthy baby.
What is PGT-M (PGD)?
Preimplantation genetic testing for monogenic/single-gene defects is a genetic test that detects the presence of a specific genetic mutation.
PGT-M is performed on an IVF embryo before transfer.
While PGT-M is not required for all patients, it offers valuable service to those who are carriers of genetic diseases.
The main benefit of PGT-M is that it significantly reduces the risk of passing hereditary disorders to the child. It helps detect and diagnose genetic anomalies that could cause disease during or after birth.
By preventing the transfer of affected embryos, PGT-M ensures that the child born through IVF will not inherit the disease.
PGT-M, or preimplantation genetic testing for monogenic/single-gene defects, was previously known as PGD (preimplantation genetic diagnosis).
How Does PGT-M Work?
The PGT-M test is performed after fertilization and before the embryo transfer during IVF. In this test, genetic material (a few cells) is taken from the embryo and examined for genetic structure.
With this very small sample, embryos can be tested and screened for a specific genetic anomaly.
Important Information About PGT-M:
- It has 98% accuracy in detecting significant chromosomal abnormalities.
- It is necessary for couples at high risk of having a child with a single-gene disease.
- It can be used for most known single-gene diseases.
- It increases pregnancy success and the likelihood of having a healthy baby.
- If you decide to add PGT-M (formerly PGD) to your treatment plan, you should consult your doctor about the possible additional cost.
What is PGT-M Screening For?
The purpose of the test is to help detect and diagnose genetic anomalies that could cause disease during or after birth.
It reduces the likelihood of becoming pregnant with a child who has a genetic disorder. This increases the chances of carrying and delivering a healthy baby.
PGT-M detects several genetic disorders, including:
- Cystic Fibrosis
- Fragile-X Syndrome
- Spinal Muscular Atrophy
- Huntington’s disease
- Autosomal dominant polycystic kidney disease
- Becker muscular dystrophy
- Beta thalassemia (Mediterranean anemia)
- Charcot-Marie-Tooth disease 1A
- Muscular dystrophy
- Familial amyloid polyneuropathy
- Hemophilia A (F8)
- Hemophilia B (F9)
- Multiple endocrine neoplasia type 2a
- Myotonic dystrophy (Steinert disease)
- RhD incompatibility
- Spinal muscular atrophy
How Does the Genetic Testing Process Work?
- The aCGH or NGS test performed in the genetic laboratory ensures the selection of embryos with normal chromosomal structure.
- These methods provide detailed information about all chromosomes, unlike the older PGS methods (FISH) that could only analyze a small number of chromosomes.
- IVF centers can combine genetic information obtained from the aCGH test with general morphological evaluation to select the best embryo for transfer or freezing procedures.
- Genetically normal embryos have higher implantation success rates and fewer miscarriages. By identifying these embryos using PGS methods, pregnancy rates increase and miscarriage rates decrease.
- PGT/PGS is performed alongside IVF procedures, including ovarian stimulation, egg collection and fertilization, embryo development, biopsy, and embryo transfer.
- Embryo biopsy is mainly performed in two stages. The first is blastomere biopsy. After the egg is fertilized by sperm, the embryos are allowed to develop until the cleavage stage. Three days after fertilization, a single cell (blastomere) is taken from the developing embryo for genetic evaluation through biopsy.
- The second method, more commonly used today, is the trophectoderm biopsy method. In this method, 4-8 cells can be taken from embryos that reach the blastocyst stage (day 5). These embryos are of better quality than the 3-day embryos and have higher implantation capacities, leading to higher pregnancy rates.
- Since the number of cells and DNA obtained is greater, the analysis results are more accurate.
- Biopsied embryos are placed in special solutions and containers and sent to genetic laboratories.
- The DNA obtained from the cells is amplified using Whole Genome Amplification (WGA), and thousands of probes are used to examine the structure of these regions.
- Unlike other methods, aCGH does not require family blood samples or other preparation steps.
- Since a full genome analysis is conducted on embryos, both single-gene disease mutation screening and 24-chromosome screening are possible.
- Before starting any preimplantation genetic diagnosis or screening procedure, candidates must consult with a genetic counselor. The necessary tests should be done to confirm the patient’s diagnosis, and the benefits of PGT in solving these issues should be carefully evaluated.
What is Preimplantation Genetic Screening with Next Generation Sequencing (NGS)?
- Using aCGH, thousands of probes distributed across the genome allow for detailed information about all chromosomes.
- With developments in sequencing methods, it is now possible to effectively and affordably sequence the entire genome. This method, called Next Generation Sequencing (NGS), enables the sequencing of embryos’ genomes after amplification. Furthermore, this data is analyzed to identify chromosomal aneuploidies and can be used for PGS.
- The advantages of NGS compared to aCGH are its more detailed and accurate results, allowing for better determination of mosaicism in embryos.
