What Are the Different Types of PGT Testing?

3 types of genetic tests and what they screen for.

Preimplantation Genetic Testing (PGT) is a type of test that can be done on embryos before they are transferred to the gestational carrier to achieve pregnancy. PGT testing screens for genetic abnormalities that can lead to implantation failure, miscarriage, and birth defects.

PGT testing looks for genetic problems that show up in the embryo’s chromosomes. Genetic testing can help identify missing or extra chromosomes, single gene disorders, and rearrangement of genes. A missing chromosome can lead to monosomy disorders like Turner syndrome, whereas an extra chromosome can lead to trisomy disorders like Down syndrome. It can also identify single gene disorders like cystic fibrosis or sickle cell anemia and chromosomal rearrangements that can lead to birth defects or a miscarriage.

The Different Types of PGT Testing

There are three different types of PGT testing that can be performed on embryos during the IVF process. Each test screens for a different type of genetic abnormality.

  • PGT-A: preimplantation genetic testing for aneuploidy (screens for any missing or extra chromosomes)
  • PGT-M: preimplantation genetic testing for monogenic disorders (screens for single gene disorders that can be passed down)
  • PGT-SR: preimplantation genetic testing for structural rearrangements (screens for rearrangement of genes that can cause birth defects, miscarriage, stillbirth, or serious health issues)

Testing for Aneuploidy (PGT-A)

The goal of PGT-A is to identify an embryo that has an abnormal number of chromosomes. A healthy embryo will have 46 chromosomes, 23 from each biological parent. PGT testing that screens for aneuploidy looks for a missing or extra chromosome.

A baby missing a chromosome can be born with Turner syndrome, a condition that affects females that can cause medical or developmental problems. The effects of Turner syndrome can range from physical symptoms like short height and a wide neck to development issues like delayed puberty or a lack of ovarian development. In some cases, missing chromosomes can cause kidney trouble and heart defects.

An extra chromosome can cause miscarriage or lead to the birth of a baby with trisomy disorders. One of the most common trisomy disorders is Down syndrome, characterized by distinct physical features but also intellectual disabilities and medical problems. Other common trisomy disorders are Edwards syndrome and Patau syndrome, which come with severe health challenges that commonly lead to death within months to a year.

PGT-A is beneficial for women over 35 years old or those who have had unexplained infertility or multiple miscarriages.

Testing for Monogenic Disorders (PGT-M)

The goal of PGT-M is to identify if an embryo has an abnormality within a specific gene. These specific genetic diseases can be passed down from biological parent to child and testing for these diseases through PGT-M can help eliminate the risk of passing it down to your child.

If a disease is caused by an abnormality in a specific gene, PGT-M can help identify it. Some of the most common genetic disorders that PGT-M screens for are cystic fibrosis, sickle cell anemia, muscular dystrophy, and Huntington’s disease.

  • Cystic fibrosis is a disorder that causes severe damage to the lungs, digestive system, and other organs.
  • Sickle cell anemia affects red blood cells, causing anemia, pain, and delayed growth.
  • Muscular dystrophy causes progressive weakness and loss of muscle mass.
  • Huntington’s disease is a breakdown of the brain’s nerve cells, leading to movement, cognitive, and psychiatric disorders.

PGT-M can also test for hereditary mutations in the BRCA genes. Healthy BRCA genes work as tumor suppressors, keeping breast and ovarian cells from “growing and dividing too rapidly or in an uncontrolled way.” When there are hereditary mutations in the BRCA genes, there is an increased risk for breast, ovarian, and other cancers.

PGT-M can be most beneficial for biological parents that have a family history of genetic disorders.

Testing for Structural Rearrangements (PGT-SR)

The goal of PGT-SR is to identify embryos that have chromosomal structural rearrangements so that they are not transferred to the gestational carrier. These rearrangements can be inherited or happen spontaneously. Some carriers of these structural rearrangements can be healthy, leading parents to be unaware they are carriers until they try to have children. Embryos with an abnormal structure are less likely to result in live birth.

PGT-SR is an effective way to identify an embryo with rearranged genes that can lead to implantation failures, miscarriages, or live-born infants with congenital anomalies.

IVF and PGT Testing

PGT testing is done via a biopsy of the embryo which is then analyzed in a laboratory. The embryo is then frozen to wait for the results of PGT testing. Once completed, the healthy embryo is thawed and transferred to the gestational carrier.

Because intended parents typically receive between 15-25 eggs from a donor’s fresh egg cycle, they usually have multiple embryos to work with. There’s always a small risk an embryo can be lost during the biopsy, but having multiple embryos gives intended parents peace of mind throughout the process.

For intended parents using frozen donor eggs, PGT testing is not recommended. Frozen eggs are usually sold in batches of six, and not all eggs survive the thawing process. A batch of six frozen eggs usually results in one embryo, and because PGT testing can be invasive, there’s a chance an embryo is lost during the biopsy process. Because one embryo leaves no room for error, PGT testing is not recommended in these situations.

Still Have Questions About PGT Testing?

Everyone’s fertility journey is unique. You may not need to use every form of PGT, or you may choose not to pursue genetic testing at all. Eggceptional Fertility is here to help you understand your options as you choose the best path for your family. Contact us for a free consultation today.