PGT-A describes screening embryos for chromosome abnormalities, instead of its previous name ‘PGS’, PGT-A refers to testing embryos by counting the 46 chromosomes to look for extra or missing chromosomes (“aneuploidy”). PGT-A is used to select embryos that are the most likely to implant and result in a successful pregnancy. It also reduces the chance of having a child with extra or missing chromosomes, such as Down syndrome.
PGT-M describes single-gene PGD. PGT-M is used to help individuals or couples reduce their risk to have a child with a known inherited disorder caused by mutations in a single gene (“monogenic”), such as cystic fibrosis or Huntington’s disease.
PGT-SR is different from PGT-A. In these cases the chromosome abnormalities are hereditary due to one or both parents having a balanced chromosome “structural rearrangement” (such as translocations or inversions). PGT-SR reduces the risk of having a pregnancy or child with an unbalanced structural abnormality, which involves extra or missing genetic material and typically results in a pregnancy loss.
Because the leading cause of pregnancy loss is chromosomal abnormalities in the developing fetus, PGT-A can increase the chances of a successful pregnancy by identifying chromosomally normal embryos for transfer. This article will explain the details of what PGT-A testing is, who are good candidates, associated costs, and more!
PGT-A is an embryonic procedure done during the IVF Process that checks the number of chromosomes for each embryo prior to the embryo transfer portion of IVF treatment.
A normal embryo contains 23 pairs of chromosomes, for a total of 46 chromosomes (euploid). 23 chromosomes come from the sperm and 23 from the egg.
Twenty-two of these pairs (autosomes) look the same for both males and females. However, the 23rd pair (sex chromosomes) differ between males and females. This is because females have two X chromosomes in their cells, and males have an X and a Y chromosome in their cells.
The example below shows a normal, or euploid chromosomal count on the left and an abnormal chromosomal count on the right given chromosome 10 has 3 copies as opposed to the two it should have.
Embryos with more or less than 46 chromosomes (aneuploid) can cause IVF transfers to fail, pregnancy loss, or significant health problems for your child.
PGT-A testing can increase the chances for a successful IVF transfer by ensuring embryos have the correct number of chromosomes.
The first step of PGT-A testing is performed after the ovarian stimulation, egg retrieval, fertilization, and embryo development stages of the IVF process. After embryos reach the blastocyst stage of development (approximately 5-7 days after fertilisation), a tissue biopsy is performed, and a small cell sample is taken from each embryo and frozen.
Next, the tissue samples are shipped to the genetics lab where testing will occur. Meanwhile, the embryos are frozen via vitrification, and they are stored until it is time for the frozen embryo transfer.
After the tissue sample(s) reach the genetics lab, then the PGT-A chromosomal analysis is completed. During the analysis, embryos are screened for chromosomal abnormalities.
After the analysis is completed, the genetics lab will send a genetics report detailing the status of each embryo, including the number of chromosomes, back to CRGW. One of our doctors will review the genetics report and share the results with the patient.
Based on the results outlined in the genetics report along with the input from the provider and patient, the embryologist will select the healthy embryo(s) for transfer. The selected embryo(s) will then be thawed for embryo transfer.
If there are remaining embryos, they will stay frozen and stored for use at a later time.
PGT-A testing can produce three different types of results for reach embryo: