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Preimplantation Genetic Testing

Preimplantation Genetic Testing

Preimplantation genetic testing. We always hear the term PGT testing but what actually happens during the test?? It’s always helpful to understand what exactly happens to an embryo as it progresses through the different stages of IVF. For those new to the terminology, PGT is a genetic test that takes place before embryo transfer, designed to tell you if each embryo is chromosomally healthy.

An embryo that is euploid (normal) has 23 pairs of chromosomes and has a better chance at leading to a successful live-birth than an abnormal (aneuploid) embryo. Aneuploid embryos have missing or extra chromosomes and will typically fail to implant, result in a miscarriage, or lead to the birth of a child with a chromosomal disease. ⁠

Besides the two possible PGS results we’ve already talked about– euploid and aneuploid– there’s also another: mosaic. A mosaic embryo is comprised of both euploid and aneuploid cells. While mosaicism has existed all along, PGS testing has only been able to recognize mosaicism in embryos within the past three years, so there is still a lot of research ongoing about their potential. What we know now is that about 10-15% of all embryos are mosaic.⁠

We can perform up to three types of preimplantation genetic testing on embryos during the ivf process.

  • PGT-A which screens for an abnormal number of chromosomes.
  • PGT-M is the test for individual or monogenic diseases.
  • PGT-SR tests for abnormal chromosomal structural rearrangements, like translocation or inversion

PGT begins with a biopsy of an embryo in the blastocyst stage of development. The biopsy removes 3 to 10 cells from the trophectoderm which are the outer layers of cells that will become the placenta as the embryo develops.

The biopsy does not remove any cells from the inner cell mass, which develops into the fetus. After these cells are removed, the blastocyst is frozen and stored in the lab. The biopsied cells are sent for laboratory testing. Results are typically returned in a week to 10 days following the biopsy!

No Result Embryos

Did any of your embryos return with a PGT result of “inconclusive’ or “No result”? That means that the trophectoderm biopsy sample was insufficient to be used for PGT or that it did not meet the quality control standards for analysis.⁠

A study by Cimadomo et al. (2018) showed that inconclusive results occur about 1.5-5% of the time because the cell sample is not loaded properly and the tube is actually empty, or that the sample was degraded. ⁠

Inconclusive or no result embryos have a good chance of being “normal”. A large study (Demko et al., 2016) found for women <35 there is about a 60% chance of a blastocyst being euploid (normal) to 30% by age 41. The chance of getting NO euploid (normal) embryos was about 10% for <35 and about 50% by 43.⁠

Are you struggling with the question “To Embryo Biopsy or NOT?” ⁠

Preimplantation Genetic Testing (also known as PGT-A, CCS, or PGS) is a diagnostic tool to tell your fertility doctor which embryos are likely to be chromosomally normal and therefore, which to transfer.⁠

As women age, the chance of a chromosomally normal embryo declines. Underage 30, roughly half of the embryos will be normal, and most young women find multiple euploid embryos after testing. Overage 40, 1/3 to 1/2 of all women will not find a viable embryo after PGT-A.⁠

Euploid embryos are most likely to lead to living birth and should be transferred first. Embryos that are mosaic can still lead to living birth, but depending upon the type, do so less often, and carry some risk. Embryos that are aneuploid almost never lead to live birth and if they do, carry a major risk the child will be unhealthy.⁠

PGT typically costs $5,000 can help to avoid:⁠

-FailedFET (each costs $3,000 to the patient)⁠

-Miscarriages (each cost $5,000 to the insurer, which pales in comparison to the emotional pain they cause patients)⁠

-Multiple gestation births from transferring back more than one embryo (twin deliveries cost $100,000 and triplet deliveries cost $500,000)⁠.

Canadian PGT Guidelines

Preimplantation genetic testing for aneuploidy: A Canadian Fertility and Andrology Society Guideline 

1. Maybe offered to patients to assist with the selection of the best embryo for transfer.
2. In patients with two or more blastocysts available for biopsy, PGT-A can improve the likelihood that a transferred embryo will lead to a viable pregnancy.
3. Offering PGT-A with eSET reduces the risk of multiple pregnancies, may improve implantation rates, and may decrease the risk of EPL per embryo transfer in select populations at higher risk of aneuploidy.
4. PGT-A has largely included good-prognosis patients with multiple blastocysts available.5. use of PGT-A in poor-prognosis patients, who may have difficulty producing blastocysts for testing.
6. A paucity of evidence on the effect of PGT-A on the critical outcome of cumulative LBR (CLBR) per cycle started.
7. The current data do not support the universal use of PGT-A for all patients undergoing IVF.
8. Future research should also consider broader issues such as economic costs, patient satisfaction, correlation with prenatal genetic testing, and long-term follow-up studies on the health of children born after PGT.
9. Other technical issues confounding the field include diagnostic inaccuracy and mosaicism.
10. Patient counseling and informed consent before undertaking PGT-A should acknowledge the known limitations of the technology and gaps in knowledge