By Sonia Albero Amorós (Gynaecologist – Reg. No. 030311380).
PGT-A involves taking a biopsy from the embryo, usually at the blastocyst stage, around day 5 or 6 of development. At this point, two groups of cells can be distinguished: the inner cell mass, which will develop into the fetus, and the trophectoderm, which mainly contributes to the formation of the placenta.
An embryologist removes a small number of trophectoderm cells, which are sent to a genetics laboratory for chromosomal analysis. One of the most widely used methods is next-generation sequencing (NGS), which can assess all the chromosomes in the sample. While the analysis is carried out, the embryo is vitrified and stored until the result is available.
The laboratory can then classify embryos as euploid, aneuploid or, in some cases, mosaic, where the sample contains a mixture of cells with different chromosomal complements. It is important to remember that PGT-A is an embryo selection test, not a guarantee of pregnancy. Knowing that an embryo is euploid provides additional information, but its ability to implant also depends on other factors.
When a couple have undergone several assisted reproduction treatments, experienced pregnancy loss or are starting treatment at an age when the risk of chromosomal abnormalities in embryos is higher, they often wonder whether it is possible to learn more about their embryos before transferring them to the uterus.
This is where PGT-A, or preimplantation genetic testing for aneuploidy, comes in. This technique assesses whether an embryo has the expected number of chromosomes before a decision is made about transferring it. However, PGT-A does not test for every possible genetic condition. It primarily looks for extra or missing chromosomes. An embryo with the expected number of chromosomes is described as euploid, whereas an embryo with an abnormal number is described as aneuploid.
In certain circumstances, this information can help determine which embryo to transfer. However, PGT-A is not routinely recommended for everyone undergoing IVF. Its use should always be assessed in light of the patient's age, reproductive history and number of available embryos.
There is no single situation in which PGT-A should always be performed. Its usefulness must be assessed individually, as the potential benefit is not the same for every patient.
As a woman's age increases, so does the likelihood that her eggs will give rise to embryos with an abnormal number of chromosomes. Advanced maternal age is therefore one of the circumstances in which PGT-A may be considered more frequently, particularly when several blastocysts are available for testing.
The risk of aneuploidy rises progressively with age. The usefulness of PGT-A also depends on ovarian reserve and the number of embryos obtained. For older women, selecting a euploid embryo may help avoid some transfers of aneuploid embryos, which are less likely to develop normally and carry a higher risk of miscarriage.
A substantial proportion of miscarriages in the first trimester are associated with chromosomal abnormalities in the embryo. When a woman or couple have experienced several pregnancy losses, they may therefore consider whether PGT-A could help select euploid embryos before another transfer.
Available evidence suggests that PGT-A may reduce the risk of miscarriage in some patient groups. However, it has not yet been clearly demonstrated that it increases the cumulative likelihood of a live birth for all couples experiencing recurrent miscarriage. Before recommending the test, it is therefore advisable to investigate possible causes of the losses and consider factors such as the woman's age, ovarian reserve and the number of embryos likely to be obtained.
When several embryo transfers have not resulted in an ongoing pregnancy, one possible explanation is that some of the embryos transferred had chromosomal abnormalities. In these circumstances, PGT-A may be considered as one element of the assessment, as it provides information on the chromosomal status of blastocysts before deciding which one to transfer.
However, implantation failure can have many causes and is not always related to an embryo's chromosomal make-up. PGT-A should therefore not be seen as an automatic solution following several unsuccessful attempts, but rather as an option to consider as part of a broader assessment of the patient's circumstances.
In some cases of severe male-factor infertility, it may be particularly important to investigate the underlying cause and assess whether an associated genetic abnormality is present. However, severe male-factor infertility alone does not necessarily indicate a need for PGT-A. Before making a decision, specific genetic tests in the male partner may be required to determine whether there is an increased risk that warrants a particular approach.
The main purpose of PGT-A is to provide more information about embryos before transfer. One benefit is that it can help avoid transferring embryos identified as aneuploid, which are less likely to implant successfully and more likely to result in miscarriage.
When more than one blastocyst is available, knowing which ones are euploid can therefore help establish a more informed order of transfer and reduce the number of transfers involving embryos with a low likelihood of resulting in an ongoing pregnancy. Available evidence also indicates that PGT-A may reduce miscarriage risk in certain patient groups, which may be particularly relevant for older women or those with a history of pregnancy loss.
However, it is important to emphasise that PGT-A does not increase the number of chromosomally normal embryos a patient produces or guarantee a higher cumulative live birth rate. Rather than viewing it as a technique that improves every IVF outcome, it should be regarded as an embryo selection tool that may offer benefits for particular patient groups.
Actualmente la biopsia suele realizarse en fase de blastocisto y se toman unas pocas células del trofoectodermo, sin extraer células de la masa celular interna que dará lugar al futuro feto. La experiencia acumulada con esta técnica indica que la biopsia de trofoectodermo realizada por profesionales experimentados tiene un impacto bajo sobre la viabilidad del embrión. Consulta nuestras tecnologías de laboratorio y el proceso de Fecundación In Vitro con PGT-A.
También hay que tener en cuenta las limitaciones propias del análisis. La biopsia estudia únicamente una pequeña muestra de células y puede obtener resultados mosaico o, en algunos casos, resultados no concluyentes. Por este motivo, el PGT-A debe realizarse en laboratorios con experiencia, como el de IVF-Life, y siempre acompañado de un adecuado asesoramiento antes de tomar decisiones sobre los embriones.
Nowadays, the biopsy is usually performed at the blastocyst stage. A small number of cells are taken from the trophectoderm, without removing cells from the inner cell mass that will develop into the fetus. Experience with this technique indicates that trophectoderm biopsy carried out by experienced professionals has a low impact on embryo viability. Explore our laboratory technologies and the IVF with PGT-A process.
The limitations of the analysis must also be taken into account. A biopsy examines only a small sample of cells and may produce a mosaic result or, in some cases, an inconclusive result. For this reason, PGT-A should be performed by experienced laboratories, such as IVF-Life, and always accompanied by appropriate counselling before decisions are made about embryos.
The time needed to obtain results depends on the genetics laboratory, the method used and how each centre operates. During this period, blastocysts remain vitrified. Once the results are received, the medical team can plan the transfer of the selected embryo in a subsequent cycle.
This means that IVF treatment with PGT-A does not usually involve a fresh embryo transfer a few days after egg collection. Instead, the process takes place in two stages: first, the embryos are obtained, biopsied and vitrified; subsequently, the endometrium is prepared for embryo transfer.
After testing, it is possible that none of the biopsied embryos will be classified as euploid. This becomes more common with increasing maternal age, as the proportion of eggs that may give rise to embryos with chromosomal abnormalities also rises. If this happens, an embryo classified as aneuploid will not be transferred simply to complete the treatment. The medical team will review the results and explain the available options in light of the individual circumstances. Depending on the patient's age, ovarian reserve, number of embryos obtained and previous treatments, another stimulation cycle may be considered in an attempt to obtain more embryos.
Practice Committee of the American Society for Reproductive Medicine.
The use of preimplantation genetic testing for aneuploidy: a committee opinion.
.
2024;
421-434
Documento de recomendaciones clínicas de la Sociedad Americana de Medicina Reproductiva sobre el uso del diagnóstico genético preimplantacional para aneuploidías (PGT-A).:
https://www.asrm.org/practice-guidance/practice-committee-documents/the-use-of-preimplantation-genetic-testing-for-aneuploidy-a-committee-opinion-2024/
Junhao Yan, Yingying Qin, Han Zhao, Yun Sun, Fei Gong, Rong Li.
Live Birth with or without Preimplantation Genetic Testing for Aneuploidy.
.
2021;
2047-2058
Ensayo clínico multicéntrico que compara los resultados reproductivos de pacientes sometidas a fecundación in vitro con y sin PGT-A:
https://pubmed.ncbi.nlm.nih.gov/34818479/
Edith Coonen, Carmen Rubio, Dimitra Christopikou, Eftychia Dimitriadou, Julia Gontar, Veerle Goossens.
ESHRE PGT Consortium good practice recommendations for the detection of structural and numerical chromosomal aberrations.
.
2020;
hoaa017
Recomendaciones de la Sociedad Europea de Reproducción Humana y Embriología sobre las técnicas utilizadas para detectar alteraciones cromosómicas numéricas y estructurales en embriones.:
https://pubmed.ncbi.nlm.nih.gov/32500102/
Practice Committees of the American Society for Reproductive Medicine and the Genetic Counseling Professional Group.
Clinical management of mosaic results from preimplantation genetic testing for aneuploidy of blastocysts: a committee opinion.
.
2023;
973-982
Documento de recomendaciones clínicas sobre la interpretación y el manejo de resultados de mosaicismo cromosómico obtenidos mediante PGT-A.:
https://pubmed.ncbi.nlm.nih.gov/37678731/
Human Fertilisation and Embryology Authority.
Pre-implantation genetic testing for aneuploidy (PGT-A).
.
2020;
nformación de la autoridad británica de fertilización y embriología sobre el funcionamiento del PGT-A, sus posibles beneficios, riesgos y limitaciones.:
https://www.hfea.gov.uk/treatments/treatment-add-ons/pre-implantation-genetic-testing-for-aneuploidy-pgt-a/
Filipa Carvalho, Edith Coonen, Veerle Goossens, Georgia Kokkali, Carmen Rubio, Madelon Meijer-Hoogeveen.
ESHRE PGT Consortium good practice recommendations for the organisation of PGT.
.
2020;
hoaa021
Recomendaciones del Consorcio PGT de ESHRE sobre la organización de los programas de diagnóstico genético preimplantacional:
https://pubmed.ncbi.nlm.nih.gov/32524036/
Georgia Kokkali, Giovanni Coticchio, Fernando Bronet, Catherine Celebi, Danilo Cimadomo, Veerle Goossens.
ESHRE PGT Consortium and SIG Embryology good practice recommendations for polar body and embryo biopsy for PGT.
.
2020;
hoaa020
Documento de recomendaciones técnicas de ESHRE sobre la biopsia embrionaria y de cuerpos polares utilizada en las pruebas genéticas preimplantacionales:
https://pubmed.ncbi.nlm.nih.gov/32500104/
ESHRE Guideline Group on Recurrent Pregnancy Loss.
ESHRE guideline: recurrent pregnancy loss: an update in 2022.
.
2023;
hoad002
Guía clínica de la Sociedad Europea de Reproducción Humana y Embriología sobre el diagnóstico y tratamiento de los abortos de repetición:
https://www.eshre.eu/Guidelines-and-Legal/Guidelines/Recurrent-pregnancy-loss
Santiago Munné, Brian Kaplan, John L. Frattarelli, Tim Child, Gary Nakhuda, F. Nicholas Shamma.
Preimplantation genetic testing for aneuploidy versus morphology as selection criteria for single frozen-thawed embryo transfer in good-prognosis patients: a multicenter randomized clinical trial.
.
2019;
1071-1079.e7
Ensayo clínico multicéntrico que compara la selección embrionaria mediante PGT-A con la selección basada en criterios morfológicos convencionales.:
https://pubmed.ncbi.nlm.nih.gov/31551155/
Martine De Rycke, Antonio Capalbo, Edith Coonen, Giovanni Coticchio, Francesco Fiorentino, Veerle Goossens.
ESHRE survey results and good practice recommendations on managing chromosomal mosaicism.
.
2022;
hoac044
Recomendaciones de ESHRE sobre la identificación, interpretación y manejo del mosaicismo cromosómico detectado mediante pruebas genéticas preimplantacionales:
https://pubmed.ncbi.nlm.nih.gov/36349144/
Privacy Policy
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Contact with the Data Protection Officer: dpo@ivf-life-group.com
DATA CONTROLLER: IVF Spain Madrid (hereinafter IVF-Life)
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