Why test embryos?

Genetic testing of embryos aims to thoroughly screen embryos for genetic diseases that may cause abnormal development or failure to implant after transfer to the uterus. A large number of alterations in the genetic material can lead to the appearance of developmental defects, most of which can cause the death of the foetus (so-called lethal defects). The procedure therefore makes it possible to transfer an embryo into the uterus in which no defects are found. Testing not only increases the chances of a healthy pregnancy, especially in difficult cases of infertility and recurrent miscarriages. They also improve the psychological comfort of the parents. The waiting time for the result of a genetic embryo test can be around two weeks.

Genetic testing of the embryo before IVF

Preimplantation genetic testing is carried out during the IVF procedure, specifically at the end of embryo culture. When the embryo reaches the blastocyst stage, a very experienced embryologist extracts a fragment of the trophoectoderm with a biopsy pipette. The fragment thus extracted, suitably protected, is then sent to the genetics laboratory, where the genetic material is analysed.

A common question from patients is whether such micromanipulation adversely affects embryo development. It should be emphasised that embryo fragment retrieval is one of the most difficult procedures in the IVF laboratory and, with current advanced techniques, there is a minimal risk of blastocyst degeneration after biopsy.

Genetic testing of the embryo before IVF is performed on the fifth day after fertilisation in the laboratory. After the biopsy procedure, the embryos are safely stored (vitrified) until the genetic test result is received. Once the test result is received, healthy embryos are warmed and can be transferred into the patient's uterus.

When PGT-A and when PGT-M?

Many patients wonder how PGT-A (formerly PGS) differs from PGT-M (formerly PGD). These tests have one and the same purpose: to exclude the carriage of genetic defects. The difference between PGT-A, the so-called test for the detection of aneuploidies, and PGT-M relies on the type of genetic defects detected by both tests.

PGT-A

The PGT-A preimplantation test detects numerical chromosome alterations in the embryo karyotype, known as aneuploidies. It makes it possible to detect diseases caused by changes in the number of certain chromosomes, such as Down's syndrome, Turner's syndrome or Patau's syndrome, or other defects causing fetal demise. It is an extremely modern and precise test method, based on the use of advanced techniques for sequencing the human genome, which allows direct and accurate reading of genetic information.

In the case of structural changes in the parents' karyotypes, so-called chromosome rearrangements such as translocations, deletions, duplications, a PGT-SR test is performed.

PGT-M

By contrast, PGT-M test is performed to look for variations within a single gene that cause so-called monogenic (single-gene) diseases. PGT-M is primarily performed when one or both parents have the disease or are carriers (when they themselves do not have the disease but have a defective copy of the gene) of a monogenic genetic disease. Such diseases include cystic fibrosis or fragile X syndrome.

When to perform preimplantation embryo genetic testing?

Couples who will wish to perform genetic diagnosis on an embryo prior to transfer should have an extensive genetic history with a geneticist after referral by the attending physician. They will be the ones to suggest the type of test to patients: PGT-A, PGT-SR or PGT-M.

Indications for pre-implantation diagnosis of the embryo:

couples with a history of habitual (recurrent) miscarriages,
couples who have a child with a genetic disorder (e.g. Down's syndrome, cystic fibrosis),
couples in which one or both partners have an abnormal karyotype,
couples in which at least one partner is a carrier or has a specific monogenic disease (including a family history of such a disease),
women who are over the age of 35.

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Dr Marta Bogucka

Head of embryology laboratory InviMed clinics in Warsaw, senior embryologist. Graduate of the Warsaw University of Life Sciences (SGGW) with extensive scientific achievements, as confirmed by her PhD degree obtained in 2019.