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Preimplantation Genetic Testing: What is it and do I need it?

Updated: Nov 21, 2022


With in vitro fertilization, we can access the developing embryo. As the name implies, genetic

testing takes place before the embryo (blastocyst) would normally implant into the uterine lining.

Implantation in humans takes place between six and 12 days after ovulation, but normally about

day nine.

After the in vitro fertilization takes place the embryos created are cultured for up to six days.

Normally, about day 5 the embryologist will take a sample of the trophoblast (part that forms the

placenta). This sample will be sent to a laboratory for genetic testing. At this point all the

embryos will need to be frozen until results are obtained. Results can be as soon as two weeks

but normally more like a month depending on the laboratory. Using any of these tests means

fresh embryo transfer cannot take place.

There are three basic types of preimplantation genetic testing (PGT).

1) PGT-A. This test is for determination of aneuploidy in the embryo. Aneuploidy is

defined as an abnormal number of chromosomes either too many or not a pair. A well-

known example is Down’s syndrome where the person has three copies of chromosome

21. More about this test at the end of this section.

Who should test for PGT-A

Women who have had two or more miscarriages

Those who have experienced several failed IVF cycles

Women who are age 35 or greater

Those who want to select the gender of their child.

2) PGT-M. This is commonly known as preimplantation genetic testing for monogenic

diseases. If there is a known genetic disease carried by either the father or mother, this

test would be implicated. This test is called for people who are at high-risk of passing

on a specific single gene disorder. Some examples of when PGT-M testing is

prudent below.

Who should test for PGT-M

If one of the couple is a carrier of an X-linked condition such as Duchenne Muscular Dystrophy

Your partner or you have an autosomal dominant condition such as Huntington disease

Your partner and you have the same autosomal recessive condition such as Cystic fibrosis

One or both of the couple has a mutation associated with a hereditary cancer syndrome such

BRCA1 & 2 (breast cancer)

3) PGT-SR. This test is preimplantation genetic testing for structural chromosomal

rearrangements. These chromosomal rearrangements are normally caused by balanced

translocations and inversions.

Who should test for PGT-SR

People who have a chromosome rearrangement. If you or your partner are carriers of a

chromosomal Robertsonian translocation, a reciprocal translocation or inversion. It would be

wise to have this test before embarking on family creation.


Should we have PGT-A done on our embryos??


Not necessarily. The most recent medical literature suggest it is not warranted unless the egg donor is 35 years old or more.


Euploid or not??*:

How do I know if my embryos are euploid? This is answered by Preimplantation Genetic

Testing (PGT-A). This test adds to your cost, but may in the end save you money by reducing

the number of embryo transfers necessary. In the ESP program, PGT-A testing adds about

$3500-$5500 to the total cost. If you want to select the gender of your child, PGT-A is

necessary.

Some clinical studies demonstrate a benefit to using PGT-A to reduce time and cost. Later

medical studies shed doubt on the benefits with some showing a detriment.

2018 medical study showing benefits of PGT-A.


Preimplantation genetic testing for aneuploidy is cost-effective, shortens treatment time, and reduces the risk of failed embryo transfer and clinical miscarriage

A 2020 study concluding the opposite.

Nicole Doyle, Michelle Gainty, Allison Eubanks, Joseph Doyle, Heidi Hayes, Michael Tucker, Kate Devine, Alan DeCherney, Michael Levy, Samad Jahandideh, Micah Hill

Hum Reprod. 2020 Nov; 35(11): 2548–2555. Published online 2020 Oct 15. doi: 10.1093/humrep/deaa219


A 2022 study showing PGT-A is slightly detrimental.

Does PGT-A improve assisted reproduction treatment success rates: what can the UK Register data tell us?

Stephen A. Roberts, Jack Wilkinson, Andy Vail, Daniel R. Brison

J Assist Reprod Genet. 2022 Sep 21 : 1–8. doi: 10.1007/s10815-022-02612-y


A 2020 review on the topic of PGT-A and PGT-ST

Preimplantation Genetic Testing for Chromosomal Abnormalities: Aneuploidy, Mosaicism, and Structural Rearrangements

Manuel Viotti

Genes (Basel) 2020 Jun; 11(6): 602. Published online 2020 May

29. doi: 10.3390/genes11060602


Most recent studies state that PGT-A is not necessary unless the egg donor is over 35. There is some controversy about using this test. Consult with us if you are confused.

*Euploid means the embryo has the correct number of chromosomes. Aneuploidy means there are too many or too few chromosomes. Trisomy 21 is a condition where there are three copies of chromosome 21. Individuals born with three chromosome 21 have a condition known as Downs Syndrome.


More Information:

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7257212/

Based on its own website, the Preimplantation Genetic Diagnosis International Society (PGDIS) is a professional society of 262 worldwide members (http://pgdis.org/docs/members2020_0211.pdf), primarily composed of clinicians and laboratory geneticists instrumental in guiding and promoting PGT-A practice. It recently published an updated Position Statement (PGSIS-PS) on the subject of PGT-A [6], which sparked the formation of the International Do No Harm Group in IVF (IDNHG-IVF) to formulate a response. The IDNHG-IVF is a consensus-body of clinicians, embryologists and basic scientists, concerned with advocation of insufficiently validated add-ons to IVF. Because of an important recently published study [7] with two accompanying commentaries [8, 9], this communication appears timely.


Summarizing the argument


The primary objectives of this communication are to voice concerns regarding statements made in the latest PGDIS-PS regarding the nonjudicial usage of PGT-A. Here presented conclusions are based on six difficult to refute facts: (i) The hypothesis that PGT-A improves pregnancy and live birth chances in association with IVF and reduces miscarriages, appears no longer sustainable [7, 10]. (ii) That PGT-A does not improve IVF outcomes in good-prognosis patients, suggests that in poorer-prognosis patients PGT-A, likely, adversely impacts outcomes, as first already reported by Mastenbroek et al. over a decade ago [11]. Loss of false-positively diagnosed embryos is more significant in poorer-prognosis patients with small embryo numbers. (iii) Hundreds of chromosomally healthy births following transfer of, by PGT-A reported to be chromosomal-abnormal embryos (“mosaic” and “aneuploid”), have been reported [12], confirming the discarding of embryos with considerable normal pregnancy potential after false-positive PGT-A diagnoses, recently also pointed out by Paulson [5]. (iv) Demonstration that aneuploid embryos have the capacity to self-correct downstream from the blastocyst stage, was first reported in the mouse [13] and, recently confirmed in the human embryonic cell lineage and in human gastruloids [14]. In mice [13] and humans [14], ability to self-correct is significantly lower in extraembryonic trophectoderm than in the embryonic cell lineage of the inner cell mass. Trophectoderm, therefore, for biological reasons alone, cannot reliably represent the inner cell mass. (v) A single trophectoderm biopsy of on average 5–6 cells, as is currently the practice in PGT-A at blastocyst stage, mathematically cannot represent the whole embryo [15]. (vi) In clinical medicine, the responsibility to establish validated evidence in support of a proposed treatment and/or test, rests with proponents of treatments/tests, mandating that such evidence exists before such treatments/tests are integrated into routine clinical practice.

Without further improvements in PGT-A, the IDNHG-IVF here suggests that current results obtained with PGT-A should be viewed critically. In opposition to some of the recommendations for laboratory and/or clinical practice proposed by the PGDIS-PS, the IDNHG-IVF, therefore, advocates limitation on PGT-A usage.


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