Preimplantation Genetic Testing (PGT) is performed before embryo transfer during In-vitro Fertilization (IVF) to identify genetic defects in embryos created through IVF before transferring them to the uterus. This type of testing is often recommended because it increases the chance of successfully implanting the best possible embryo (or embryos) for the production of a live birth with a healthy baby. It can also be an opportunity to choose the sex of your baby.

To differentiate the specific types of embryo testing, PGT is divided into three subtypes, defined as:

  1. PGT for Aneuploidies (PGT-A)
  2. PGT for Monogenic or Single-Gene Defects (PGT-M)
  3. PGT for Chromosomal Structural Rearrangements (PGT-SR)


What is PGT-A?

PGT-A is sometimes referred to as PGS, or preimplantation genetic screening. PGT-A is used to determine whether the cells in an embryo contain the normal number of chromosomes, which is 23 pairs or 46 chromosomes total. After an embryo grows in the lab, it is usually biopsied on day 5 or 6 (blastocyst stage) and a few embryo cells are then sent to a genetic testing lab which uses technology to count the number of chromosomes within each cell. Embryos with a normal number of chromosomes are “euploid” and those with an abnormal number are “aneuploid.”

Who benefits from PGT-A?

PGT-A is becoming a standard part of every IVF cycle at many leading fertility practices and across the world. It is also recommended in certain cases to increase the chance of IVF success, or to help diagnose and overcome hidden causes of infertility in:

  • Women of advanced maternal age (typically 35 or older)
  • Women or couples with unexplained infertility
  • People who have experienced previous IVF failure
  • Women who have had recurrent miscarriages
  • Women who have had a previous abnormal pregnancy or a child with a genetic condition


What is PGT-M?

PGT-M is a genetic test performed on embryos produced through IVF, with the goal of identifying and transferring an embryo free of the condition. PGT-M is sometimes referred to as PGD, or preimplantation genetic diagnosis. Rather than counting chromosomes in cells taken from embryos, as is done with PGT-A, PGT-M examines specific genes, searching for a specific genetic defect that is known to run in your family or for which you are known to be a carrier.

Who benefits from PGT-M?

PGT-M is appropriate for those who know they are at increased risk of having a child with a specific genetic condition. You might consider PGT-M through genetic testing labs if you and/or your partner are carriers of, or are affected with, a single-gene disorder or hereditary cancer syndrome, such as:

  • Cystic fibrosis
  • Fragile X syndrome
  • Huntington’s disease
  • Breast or ovarian cancer (BRCA1 and 2)


What is PGT-SR?

PGT-SR is a genetic test that can determine whether embryos created through IVF have chromosomes that are arranged abnormally or are not sized correctly. Generally, embryos with such abnormalities do not result in successful pregnancies.

PGT-SR tests the embryos for specific structural rearrangements for which you and/or your partner are at risk. Such rearrangements can increase the chance of implantation failure, miscarriage or the birth of a baby with a chromosome disorder.

Who benefits from PGT-SR?

PGT-SR is recommended for people who are carriers of a balanced translocation or inversion and wish to conceive a baby.

People who carry a balanced translocation or inversion have the correct amount of genetic information, but some of this information is in a different orientation than expected. Although most carriers of balanced chromosome rearrangements are healthy, they are at higher risk of producing embryos with an abnormal amount of genetic material (known as an unbalanced rearrangement). Adults often discover that they are carriers only when they try to have children and have trouble getting or staying pregnant.

PGT-SR may be recommended if you or your partner is a carrier for a:

  • Reciprocal translocation: Pieces of chromosomes have switched places.
  • Robertsonian translocation: Chromosomes link together and create an abnormal chromosome count. This can cause conditions including trisomy 13 and uniparental disomy (UPD). This type of rearrangement may also result in translocation Down syndrome.
  • Inversion: Part of a chromosome is turned upside down and reinserted back into the chromosome.

The first international standardized definitions for reporting ART procedures were published by the International Committee for Monitoring Assisted Reproductive Technologies (ICMART) in 2006 as the ICMART Glossary on ART Terminology. This document was a result of work started at a meeting in Geneva, Switzerland in 2001, where experts in the field met to define the 53 terms used within the consensus statement.

In 2017, the second revision of the International Glossary of Infertility and Fertility Care was published, defining a total of 283 medical terms used in ART. This latest edition was the result of five working groups and 20 international participating organizations involved in ART, including the American Society for Reproductive Medicine, the European Society of Human Reproduction and Embryology and the March of Dimes. The purpose of this glossary is to provide “a consensus and evidence-driven set of terms and definitions that can be used globally to provide quality care and ensure consistency in registering specific fertility care interventions plus more accurate reporting of their outcomes.”

One of the major terminology changes was to replace both the terms PGD and PGS, also called “comprehensive chromosome screening,” or CCS, with the umbrella term of PGT. PGT now encompasses all types of genetic testing on embryos.

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