Do PGT and PGD Mean the Same Thing?

by | Sep 17, 2018 | Current Technology | 0 comments

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Whether watching reruns of “ER” or the latest episode of “Grey’s Anatomy,” viewers are expected to learn a handful of acronyms for medical terminology to keep up with the flurry of dramatic dialogue. While abbreviations such as DNR and STAT can be easily recognized and understood, Hollywood rarely includes acronyms that we commonly use in the field of assisted reproductive technology (ART).

To further complicate matters, medical terminology and the corresponding acronyms often change in ART, as this relatively new field develops rapidly. In fact, just as SharingHealthyGenes.com was launched to provide education on issues related to “preimplantation genetic diagnosis,” or PGD, the medical field has shifted its language to replace this term with “preimplantation genetic testing,” or PGT.

How Is Medical Terminology Defined for ART?

Before we dive into the details of PGT, it’s helpful to understand how medical terminology is defined in reproductive medicine and why it changes over time.

As new technology develops, new terminology must be created to describe that technology. The specific words used can vary between researchers and clinicians, or from country to country. Using different terminology can cause confusion among healthcare professionals and patients, with potentially harmful consequences. Consensus among medical terms is also important for the public and policy-makers as they determine ethical, legal and social implications of the technology, especially when it involves reproductive medicine where laws may limit certain procedures from being offered in a country.

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.”

What Is the New Terminology for PGD?

One of the major terminology changes was to replace both the terms PGD and preimplantation genetic screening (PGS), also called “comprehensive chromosome screening,” or CCS, with the umbrella term of PGT. PGT now encompasses all types of genetic testing on embryos. All PGT requires in vitro fertilization (IVF), followed by embryo biopsy, genetic testing on the biopsied sample and transfer of selected embryos into the uterus based on the results of genetic testing.

There are three subtypes of PGT defined in the glossary:

Previous term

Consensus term

Consensus acronym

Definition

PGS or CCS

PGT for aneuploidies

PGT-A

Counts all 46 chromosomes to look for “aneuploidy”: extra or missing chromosomes. Used to select the embryos most likely to implant and result in a successful pregnancy. It also reduces the chance to have a child with extra or missing chromosomes that are not inherited, such as Down syndrome.

PGD

PGT for monogenic/ single gene disorders

PGT-M

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 disease.

PGD

PGT for chromosome structural rearrangements

PGT-SR

Used to help individuals who have balanced chromosome “structural rearrangements” — such as translocations or inversions — to reduce the risk of having a child with an unbalanced structural abnormality, which involves extra or missing genetic material typically resulting in a pregnancy loss.

While the ART community has shifted to using the term PGT, it takes some time for healthcare professionals in other specialties, policymakers and the public to become aware of this new terminology. In the meantime, if a TV doctor happens to say, “Let’s talk about this couple’s option of PGT,” you can confidently say, “I know that one!”

Leslie is a board-certified clinical genetic counselor and Program Manager for the preimplantation genetic testing (PGT) program of the ORM Genomics team and the Project Manager for SharingHealthyGenes.com. She completed her Bachelor’s degree at DePauw University and her Master’s degree in Genetic Counseling at the University of Texas Graduate School of Biomedical Sciences at Houston. Since graduating in 2000, she has worked as a clinical genetic counselor in several specialties including prenatal, pediatric and cancer genetics and has been very involved with the National Society of Genetic Counselors.

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