Preimplantation genetic testing
Advances in fertility technology can increase the chances of conception of a genetically healthy baby through preimplantation genetic testing (PGT). PGT testing looks for chromosomal abnormalities that may lead to miscarriage or genetic disorders. Alongside our personalized treatment plans, PGT can help you achieve your family-building goals.
Types of preimplantation genetic testing
Preimplantation genetic testing for aneuploidies (PGT-A)
Embryos with extra or missing chromosomes are considered aneuploid (abnormal) and are not recommended for transfer. PGT-A determines which embryos have the correct number of chromosomes and allows fertility specialists to preferentially transfer one of those embryos to give the best chance for implantation and a live birth while decreasing the risk of miscarriage. Your physician may recommend in vitro fertilization (IVF) treatment followed by PGT-A to test embryo chromosome numbers, particularly in women who are in their late 30s or early 40s or who have a history of multiple miscarriages. Embryos that test normal are referred to as euploid whereas those with an abnormal number of chromosomes are referred to as aneuploid.
What to expect
Once embryos reach the blastocyst stage on day 5 through 7 of embryo development, an embryologist will take a few cells from the embryo for genetic testing. The number of chromosomes will then be analyzed in each embryo. Since the test results usually take about 2 weeks to come back, all embryos will be cryopreserved until the results of the analysis are available. In a subsequent FET cycle, an embryologist can then thaw an embryo with the correct chromosomal number (euploid) and the physician can transfer it to the uterus.
Why test?
PGT-A can improve outcomes for patients with:
- Advanced reproductive age resulting in a higher percentage of abnormal oocytes and aneuploid embryos
- A history of miscarriage
- A history of failed in vitro fertilization (IVF) cycles
Preimplantation genetic testing for monogenic/single gene defects (PGT-M)
PGT-M is used to reduce the risk of having a child with a known inherited disorder caused by mutations in a single gene, such as cystic fibrosis, Huntington’s disease, or BRCA. Typically, you are aware you are a known carrier (diagnosed by genetic carrier screening), have a family history of a genetic disorder, or are affected yourself.
What to expect
Once fertilization occurs, the embryo will develop over the next 5 to 7 days to the blastocyst stage. An embryologist will then biopsy a small group of cells from the embryo for genetic testing. The genetic testing laboratory will likely develop specific probes to detect the genetic mutation that you would like to identify in your embryos. Then, the biopsied cells are analyzed to determine if any of your embryos are affected. Since the test results may take a few weeks to come back, all embryos will be cryopreserved. In a subsequent frozen embryo transfer (FET) cycle, an embryologist can then thaw the embryo that is normal—not affected by the genetic disorder they were screened for—and the physician can transfer it to the uterus.
Why test?
PGT-M can mitigate risks for patients:
- Who have been diagnosed with a hereditary condition
- With a family history of a diagnosed hereditary disorder
- With previous conception of a child with an inherited genetic disorder
- Who have been found to be carriers of a hereditary genetic condition along with their partner
Preimplantation genetic testing for structural rearrangements (PGT-SR)
PGT-SR is performed to identify structural rearrangements in embryos. Rearrangements occur when one or both of the parents have the right amount of DNA, but sections of chromosomes have traded places. This often results in multiple miscarriages. These can be diagnosed through a karyotype – a blood test that evaluates chromosome number and structure. A karyotype may be recommended by your doctor based on specific findings in your history or test results (for example: recurrent pregnancy loss or significant semen abnormalities).
This test is performed when there is a known chromosome rearrangement in either the male or female partner of the couple trying to conceive. The most common rearrangement is called a balanced translocation. This is where all the correct genetic material is present in the cells but a piece of 2 different chromosomes are located where the other should be found (essentially, these 2 parts of the genetic code have “switched places”). This is an issue for reproduction because a high percentage of the gametes (oocytes or sperm) will be aneuploid with too much or too little genetic material, resulting in embryos with unbalanced chromosomes.
The embryo testing process is the same as described for PGT-M and PGT-A.
Why test?
PGT-SR can mitigate risks for patients:
- Who have recurrent miscarriages due to a translocation or inversion
- Who have a balanced translocation
- Who have a chromosomal inversion
Medical contribution by:
Kate Devine, M.D.
Director of Research
