Preimplantation Genetic Testing for Aneuploidies (PGT-A)
Preimplantation genetic testing (PGT) involves embryos being screened for chromosomal abnormalities and genetic disorders. PGT is performed on embryos created through IVF before they are transferred to the woman’s uterus.
At RBA, we provide a treatment called PGT-A, formerly known as preimplantation genetic screening (PGS) or comprehensive chromosomal screening (CCS). PGT-A is an important test, as it fulfills two essential purposes:
It is used to count the number of chromosomes contained within the cells.
It is used to identify embryos with the correct number of chromosomes.
Chromosomes, and their specific number, play a key role in an embryo’s health and development. They contain all the information a cell requires to form a body and are essential for cell division. Humans have a total of 46 chromosomes, with 23 coming from the mother and 23 from the father.
When a division error occurs, a condition known as aneuploidy may occur, in which cells have too many or too few chromosomes. Some common conditions that are caused by aneuploidy include Klinefelter syndrome and Down syndrome. Children born with aneuploid disorders may be born with certain characteristics and anomalies, such as intellectual disabilities, delayed development, and specific physical characteristics. PGT-A is generally recommended for cases of recurrent pregnancy loss and advanced maternal age.
Preimplantation Genetic Testing for Structural Chromosomal Rearrangement (PGT-SR)
Certain embryos may possess the correct number of chromosomes, but structural abnormalities exist, such as deletions, duplications or rearrangements. For these prospective parents, we perform a genetic test called PGT-SR, which is used to identify specific chromosomal abnormalities in embryos.
PGT-SR allows our fertility specialists to select only the healthiest embryos for transfer, avoiding those with potential translocations. For couples with embryos impacted by these abnormalities, this test boosts the chances of having successful and healthy pregnancies. PGT-SR is generally only recommended for carriers of certain structural rearrangement types. However, you and your partner may first require genetic counseling or testing to determine if you do carry these rearrangements.
Approximately 4% of couples with recurrent pregnancy loss have a chromosome rearrangement present in one parent, such as balanced reciprocal translocations, Robertsonian translocations, inversions, and marker chromosomes.
In most cases, carriers don’t experience any apparent abnormalities. However, there may be increased risks of infertility, recurrent pregnancy loss, and the likelihood of having children with genetic abnormalities.
Preimplantation Genetic Testing for Monogenic Disorders (PGT-M)
If you and your partner are carriers of a known genetic disorder, you have up to a 50 percent chance that the disorder could be passed on to your child. PGT-M, formerly known as preimplantation genetic diagnosis (PGD), identifies embryos free of certain genetic mutations. Used in conjunction with IVF, PGT-M may take several months to complete. PGT-M greatly decreases the risk of passing on the genetic disorder to a child.
Assessment of Family History
Gathering a complete and accurate family medical history is extremely important, as genetic medicine explains more diseases. Among RBA’s genetic counseling services, we’ll work with you to compile a detailed, three-generation family history. This can help us to determine which genetic diseases may pose a risk to your pregnancy or your offspring. In some cases, the identification of at-risk diseases may lead to preventive treatment or genetic testing of embryos.
Advanced Maternal Age
As women get older, the risk of randomly-occurring chromosome abnormalities increases. These include Down syndrome, Trisomy 13/18, and many chromosomal abnormalities, which are not compatible with life and will result in failed implantation and/or early miscarriage. However, RBA’s genetic counselor can assess your risk and discuss the different options available to maximize the chance of a successful pregnancy.
Ethnicity-Based Carrier Screening
Every human is a carrier of an average of one or two genetic mutations. These can cause severe genetic disorders when two copies of the mutation are inherited, with one from each parent. Carriers are healthy and do not typically have a family history of the disease.
RBA offers a comprehensive carrier screening panel, including 23 of the most common genetic diseases across all ethnicities. In the event both parents are found to be carriers of the same disease, known as a recessive disease, it may be preventable via PGD technology. Examples of some common recessive diseases include cystic fibrosis, spinal muscular atrophy, sickle cell disease, and Tay-Sachs disease.
Education About Prenatal Screening and Testing Options
Chromosome abnormalities may still result in viable pregnancies and can be detected during pregnancy as early as 10 weeks into gestation. Prenatal testing options during pregnancy are numerous and include first-trimester screening, noninvasive prenatal testing (NIPT), chorionic villus sampling (CVS), and amniocentesis. RBA’s genetic counseling services can review the pros and cons of these different types of prenatal testing.
