Using IVF on your journey to parenthood? It might be worth your while to explore how PGT could increase your chances of a successful and healthy pregnancy.
If you’re an individual or couple exploring fertility and surrogacy solutions, odds are you’ve happened across the term, “preimplantation genetic testing (PGT).” Put simply, PGT is a process that can help mitigate the risk of genetic anomalies and increase the likelihood of a successful pregnancy and healthy baby.
What does preimplantation genetic screenings test for?
Also called IVF genetic testing, PGTs test for a variety of issues, from missing or extra chromosomes to genetic disorders and genetic abnormalities. It can also test for the gender of the child.
Preimplantation genetic diagnosis is often advised for individuals who plan on using in vitro fertilization (IVF). It allows fertility specialists to examine the embryos before implantation in the uterus. In this way, PGTs can increase the likelihood of a successful pregnancy and live birth by selecting and implanting embryos free from chromosomal or genetic abnormalities.
The benefits of PGT
Increases the odds of successful implantation
Increases the likelihood of a healthy and successful pregnancy
Reduces the risk of birth defects
Reduces the likelihood of genetic disorders and diseases being passed on to heir
Can lessen the number of IVF cycles needed
Reduces the odds of miscarriage
There are three main types of pre-implantation genetic diagnosis tests: PGT-A, PGT-M, and PGT-SR.
Pre-implantation genetic testing for aneuploidy (PGT-A)
In a typical, healthy pregnancy, an embryo will have 23 pairs of chromosomes. One chromosome for each pair comes from the egg, and the other from the sperm. In some cases though, genetic material is missing or has extra chromosomes. This is entirely natural and often occurs randomly, meaning they’re not inherited by the egg and sperm donors.
A review of 36 studies found that roughly 73% of embryos through IVF contained some sort of aneuploid cells. [1, 2] Another study placed that rate of embryos with aneuploid cells closer to 50% per IVF cycle. [3]
Research has found that embryos with anueploid cells are at a much higher risk for miscarriage in the first trimester, and are linked with higher rates of unsuccessful IVF cycles.
This type of PGT can test for:
Monosomies (missing a chromosome)
Trisomies (has extra chromosome(s))
Down syndrome
Turner’s syndrome
Klinefelter’s syndrome
The child’s gender
A note on mosaic cells
It’s important to note that PGT is based on the understanding that the 5-10 cells biopsied for examination are representative of the rest of the egg’s cells. However, in the case of mosaicism, this may not be true. The biopsy may reveal healthy cells, while there are irregular cells in the rest of the embryo, or vice versa.
Conversely, the biopsied cells may show a mixture of normal and abnormal cells in their biopsy. In these cases the embryos are typically only recommended for transfer if there are no normal euploid embryos available. [4]
Pre-implantation genetic testing for monogenic disorders (PGT-M)
Monogenic disorders refer to diseases prompted by variations in a single gene. These disorders tend to be highly inheritable. For this reason, PGT-M is typically performed when the donors (intended parents or egg/sperm donors) are known to have a genetic condition that could be passed on to their heirs. More specifically, this test is relevant for women who carry an X-linked condition, or if both donors are carriers for the same recessive condition.
These disorders can be passed down whether both or only one parent has the gene for it, so testing embryos beforehand can help select embryos for transfer that are free from the disorder.
Some disorders that PGT-M tests for includes:
Cystic fibrosis
Sickle cell anemia
Hemophilia
Down’s syndrome
Tay-Sachs disease
BRAC1 and BRAC2
Huntington’s disease
Muscular dystrophy
Fragile X syndrome
Pre-implantation genetic testing for chromosome structural rearrangements (PGT-SR)
This PGT test is performed when the chromosomes of the egg or sperm donor have been rearranged, like with inversion or translocation. Someone with either translocated or inverted chromosomes is at higher risk for creating embryos that are missing or contain extra chromosomes, such as with aneuploidy.
Embryos with inverted or translocated chromosomes are at higher risk for miscarriages and producing a child with serious health issues.
Additionally, SR abnormalities can result in children who are developmentally delayed, physically challenged, have learning disorders, or are infertile in adulthood.
Who is PGT recommended for?
Whether PGT is right for you depends on a few factors. As chromosomal aneuploidy can occur regardless of the donor’s health or genetic conditions, PGT-A can help improve the odds of a healthy successful pregnancy by selecting and implanting only the embryos free from abnormalities. For this reason, PGT-A can be advisable for anyone undergoing IVF treatment.
PGT-M and PGT-SR are typically only advised for people who have genetic conditions or structural rearrangements of their chromosomes. However, if you and your partner are unsure as to whether you’re a carrier, or are using a donor who is unsure, you may choose the extra precaution of getting tested.
You may want to consider PGT-M and PGT-SR if you are a:
Woman over the age of 35 (more mature eggs often have higher rates of abnormalities)
Woman who’s experienced unsuccessful cycles of IVF
Woman who has had a pregnancy with chromosomal abnormalities
Woman who has experienced recurrent pregnancy losses
Couple who has experienced fertility challenges in the past
Man struggling with male infertility
Patient with chromosomal disorders
Carrier of single-gene disorders
Carrier of sex-linked disorders
How is PGT performed?
On day five after the eggs are fertilized, a biopsy is performed and this material is sent to a specialized laboratory for analysis. Results are usually available in two weeks.
PGT-M and PGT-SR tests often also require additional genetic materials such as sperm, blood, and saliva.
For the PGT-M and PGT-SR tests, there is a test development phase during which the laboratory confirms whether they are able to reliably detect the health of the blastocysts with the material they’ve collected. This phase can typically take 8-12 weeks and must be completed before beginning the medications meant to stimulate egg production with IVF.
