Preimplantation Genetic Testing (PGT)

Aneuploidy is the presence of an abnormal number of chromosomes (45 or 47, for example, instead of the typical 46). The effect of additional or deleted chromosomes varies, depending on the genes affected. Perhaps the most well-known chromosome abnormality is Trisomy 21, which causes Down Syndrome.

Each embryo that undergoes PGT-A will fall into one of three categories: euploid, aneuploid, or mosaic. This information can help your Inovi Fertility Specialist select the best embryo(s) for transfer.

PGT-M specifically looks for gene characteristics such as heritable genetic mutations carried by one or both partners. Common disorders that fall into this category are Cystic Fibrosis, Huntington Disease, and Muscular Dystrophy, among others. This test is also used to select embryos with certain genetic characteristics such as gender. If a couple has a previous child affected by a genetic disorder, PGT-M can be used to screen for the same disorder. The embryos that do not carry the disorder can be transferred back to the patient’s uterus so the couple can have a healthy baby.

Structural rearrangements are changes in the size or arrangement of chromosomes, which are what hold our genetic material. If an embryo does not have the correct amount of genetic material then it is unlikely to be viable. PGT-SR tests for three types of rearrangements: Robertsonian translocations, reciprocal translocations, and inversions.

• Robertsonian translocations are when two chromosomes combine, forming one large chromosome (thus also reducing the total chromosome count).
• Reciprocal translocations occur when parts of genetic material break off of chromosomes and switch places with each other.
• Inversions are when a section of a chromosome flips upside down.

These karyotype tests are thorough in evaluating chromosomes for abnormalities. Another type of testing called fluorescence in situ hybridization (FISH) used to be commonly used as a standalone genetic test, but as it is targeted to identify abnormalities in just the 13, 18, 21, X, and Y chromosomes, it is insufficient in giving a clear picture of present abnormalities.

For couples worried about passing on one particular abnormality that affects a single gene, polymerase chain reaction (PCR) testing may be recommended. This process can duplicate a single gene from a small sample many times, and it produces clear results quickly. PCR can screen for cystic fibrosis, Huntington’s disease, Tay-Sachs disease, sickle cell anemia, and more.

Comparative genomic hybridization (CGH) was one of the first methods used in PGT to test for a complete chromosome count. Currently this test has been replaced by Next Generation Sequencing.

“NextGen” Sequencing is a faster, more cost-effective type of genetic testing than the traditional Sanger method. NGS allows for the collection of massive amounts of genetic data in just one day. While NGS is becoming more common, the Sanger method is still the “gold standard” of sequencing with 99.99% accuracy.