Preimplantation Genetic Testing
WHAT IS IT?
Preimplantation genetic testing for aneuploidy (PGT-A), previously referred to as preimplantation genetic screening (PGS), is a genetic test that assesses the chromosomal make-up of an embryo using an embryo biopsy sample. By doing this, euploid embryos can be prioritized for transfer to maximize your chances of a successful IVF cycle and healthy pregnancy.
WHO IS IT FOR?
PGT-A is appropriate for all patients undergoing IVF. Transferring euploid embryos provides a higher chance of pregnancy, a reduced risk of miscarriage, and a higher chance to have a healthy baby.
HOW DOES IT WORK?
If you decide that you’d like PGT-A with your IVF cycle, the process is simple.
IVF will be performed at your doctor’s laboratory to produce embryos.
Once your embryos reach the blastocyst stage (typically at Day 5 or Day 6 of development), an embryologist will biopsy a few cells from each embryo’s trophectoderm, the part of the embryo that goes on to form the placenta. Your embryos will be cryopreserved and stored safely at your doctor’s laboratory.
The embryo biopsy samples are sent to our genetic testing laboratory, where we use next generation sequencing (NGS) technology to analyze the DNA for aneuploidy.
Once testing is complete --within 1-2 weeks --a report is sent to your doctor’s office detailing the results of each embryo biopsy. Your doctor can then use those results to determine which embryos are suitable for transfer.
WHAT RESULTS CAN I EXPECT?
There are three types of results you can receive: 1) euploid, 2) aneuploid, or 3) mosaic.
“Euploid” indicates that no chromosome abnormalities were identified in the biopsy sample. Euploid embryos have the highest chance of leading to a successful pregnancy and healthy baby. Thus, euploid embryos are the ones prioritized for transfer.
“Aneuploid” indicates that one or more chromosome abnormalities was identified throughout the biopsy sample. Aneuploid embryos are unlikely to result in a successful pregnancy or can lead to miscarriage or the birth of a child with a serious genetic disorder. Thus, the transfer of aneuploid embryos is not recommended.
“Mosaic” indicates that one or more chromosome abnormalities was identified, but only in a portion of the biopsy sample--indicating that there is a mix of euploid and aneuploid cells in the biopsy due to an error in DNA division that occurred post-fertilization. Mosaic embryos are known to implant less often and miscarry more often than euploid embryos, but they have sometimes led to the birth of apparently healthy children. There is a risk that a mosaic embryo could lead to the birth of a child with a genetic condition. Given the risks, the transfer of mosaic embryos is generally not recommended but can be considered on a case by case basis. Approximately 15% of all samples are categorized as mosaic.
Though rare (<2% of samples), the results of PGT-A can be inconclusive. This can occur due to a variety of reasons, including poor embryo or cell quality, degraded DNA, or technical failure. When this occurs, a re-biopsy of the embryo can be considered, as a second sample returns a conclusive result the vast majority of the time. However, the option of re-biopsy should be discussed in detail with your doctor and/or the IVF lab’s embryologist(s) to determine if it is a recommended procedure.
It is important to note that PGT-A is not meant to replace standard prenatal care. Should a transfer be successful, you are encouraged to consider any prenatal genetic testing options presented to you by your OB/GYN.