If you or your partner are considering in vitro fertilization (IVF), you may have heard of preimplantation genetic testing (PGT). PGT is a new reproductive technology that can help doctors identify genetic abnormalities in embryos before implantation. It is not always necessary, but it can be a valuable tool for couples at risk of passing genetic disorders to their children.
Learn more about preimplantation genetic testing, who it’s for, and how it works.
Preimplantation genetic testing (PGT) involves testing embryos for genetic abnormalities before the embryo is transferred into the uterus.
PGT can be used to screen for a variety of genetic abnormalities, including:
PGT can help to increase the chances of a successful pregnancy and to reduce the risk of miscarriage. It can also be used to select embryos that are less likely to have a genetic disorder.
There are three types of PGT:
PGT-A, or preimplantation genetic testing for aneuploidy, is a type of genetic testing used to screen embryos for chromosomal abnormalities. This is the most common type of PGT.
Most human cells have 23 pairs of chromosomes, for a total of 46 chromosomes. However, in aneuploidy, there are extra or missing chromosomes. One extra chromosome is termed trisomy. A missing chromosome is referred to as monosomy. Most cases of aneuploidy result in miscarriage. However, some aneuploidies can result in a live birth. The most common aneuploidy that infants can survive is Down syndrome, Turner syndrome, and Klinefelter syndrome.
Examples of aneuploid chromosomes include:
Here are some factors that may make a couple good candidates for PGT-A:
PGT-M, or preimplantation genetic testing for monogenic diseases, is a type of genetic testing that screens embryos for single-gene disorders.
Examples of monogenic diseases include:
Monogenic diseases can range in severity from mild to severe. Some monogenic diseases are fatal, while others can be managed with treatment.
PGT-M can be a valuable tool for couples who risk passing on a genetic disease to their children.
Here are some of the factors that may make a couple good candidates for PGT-M:
PGT-SR stands for preimplantation genetic testing for structural rearrangements. PGT-SR screens embryos for chromosomal structural rearrangements (CSRs).
Chromosomal structural rearrangements can happen when a piece of a chromosome breaks off and attaches to another chromosome, when a piece of a chromosome flips over, or when a piece of a chromosome is duplicated (extra copies) or missing.
PGT-SR, or preimplantation genetic testing for structural rearrangements, is an option for couples where one partner has a chromosome rearrangement such as translocation or inversion.
Here are some factors that may make a couple good candidates for PGT-SR:
Embryo biopsy is when a fertility specialist or embryologist removes embryo cells for genetic testing. Couples at risk of passing genetic disorders on to their children can use embryo biopsy as a valuable tool during an IVF cycle.
The biopsy is usually performed on day 5 or 6 of the embryo’s development. The embryologist gently removes about five to 10 cells from a part of the embryo that will go on to make the placenta. Embryo biopsy has been shown to be a safe procedure that does not harm the embryo or the baby that develops from it. The cells are then sent to a laboratory for genetic testing, and the results are usually available within a few days.
An embryo biopsy is necessary for all types of PGT.
PGT, or preimplantation genetic testing, is a two-step process that includes embryo biopsy and genetic testing.
Here’s how PGT works:
The following methods are used for genetic testing in PGT:
Preimplantation genetic diagnosis (PGD) is a type of PGT that tests for a known, specific genetic disorder.
The recently modified terminology is preimplantation genetic testing for monogenic disorders (PGT-M), as above.
Preimplantation genetic screening (PGS) is a type of PGT that screens embryos for chromosomal abnormalities.
The recently modified terminology is preimplantation genetic testing for aneuploidy screening (PGT-A), as above.
PGT, PGD, and PGS all involve genetic testing of embryos before uterine implantation. However, there are some differences between these procedures.
In other words, all PGD is PGT, but not all PGT is PGD. All PGS is PGT, but not all PGT is PGS.
Like any medical procedure, preimplantation genetic testing has risks and advantages.
Risks
Advantages
The success rate of PGT depends on many factors, including maternal age, embryo quality, and the type of PGT performed. The success rate of PGT is also affected by the clinic that performs the procedure.
In general, PGT-A increases clinical and sustained implantation rates.
Below are some answers to common questions about PGT.
The time it takes to complete PGT varies depending on the type of PGT and the clinic performing the procedure. However, generally, PGT can take 1-2 weeks to complete.
Yes, PGT-A can test for Down syndrome. Down syndrome is a chromosomal disorder caused by an extra copy of chromosome 21. PGT-A can identify embryos with an extra copy of chromosome 21.
The cost of PGT can vary depending on the PGT type, the laboratory performing the testing, and the number of embryos that need to be tested.
No, PGT cannot test for autism (ASD). Autism is a complex disorder caused by genetic and environmental factors. No single gene has been identified as causing autism, so PGT cannot be used to screen for autism.
However, some research is being done on using PGT to detect ASD susceptibility genes. This research is still in its early stages, and it is unclear how effective PGT would be in identifying embryos at risk for ASD.
Deciding whether to undergo preimplantation genetic testing is a personal and important decision for couples. It is essential to consider the risks and advantages of PGT before making a final decision. A fertility specialist or genetic counselor can help couples navigate this decision-making process and provide guidance based on their circumstances.
RMA Network offers a full range of fertility services and financial options to help you start or extend your family. We can also help you navigate the decision-making process for PGT.