Preimplantation genetic testing or PGT as it’s often referred to, is a genetic test that takes place before an IVF embryo transfer, designed to tell you if each embryo is chromosomally healthy.

A normal embryo (that is euploid) has 23 pairs of chromosomes and has a better chance at leading to a successful live-birth than an 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. ⁠

And then there are mosaic embryos, which consist of both euploid and aneuploid cells. PGT 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. About 10-15% of all embryos are mosaic.⁠

Up to three types of preimplantation genetic testing can be performed 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

How is PGT performed?

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

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 and results are typically returned in a week to 10 days.

A study by Cimadomo et al. (2018) showed that inconclusive results occur about 1.5-5% of the time. This happens 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.⁠

Do you need PGT?

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. On average, under age 30, roughly half of the embryos will be normal. Over age 40, 1/3 to 1/2 of all women will not find a viable embryo after PGT-A.⁠

Euploid (normal) 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, but can help to avoid:⁠

  • FailedFET (each costs $3,000 to the patient)⁠
  • Miscarriages ⁠
  • Multiple gestation births from transferring back more than one embryo. 

The current data do not support the universal use of PGT-A for all patients undergoing IVF. Depending on where you live in the world PGT may not be offered as a regular service by your clinic. For example, some countries require that a known genetic issue exist in order for PGT to be carried out. 

If you are someone who produces very few blasts, your clinic may not want to take the risk of PGT or the freezing and thawing process damaging the embryo. They therefore may opt to do a fresh transfer instead. 

As always, discuss your options and concerns based on your specific diagnosis with your practitioner.