Clínica Fertia

What is PGT? Preimplantation Genetic Testing

Have you heard of the Preimplantation Genetic Test? PGT is a test to analyze embryonic DNA and determine genetic anomalies. It is a very early prenatal test that allows us to carry out embryo selection, increasing the chances of implantation.

With this pre-implantation genetic test, we can analyze anomalies caused by a mutation in a single specific gene, monogenic anomalies (PGT-M), or chromosomal anomalies, either structural anomalies caused by a lack or excess of a fragment of the chromosome (PGT-SR), or anomalies in the number of chromosomes (PGT-A).

In Assisted Reproduction we use PGT as a tool for embryo selection after an in vitro fertilization cycle. When making this selection of the embryo to be transferred we have to take into account three fundamental aspects:

  • Viability of the embryo, capacity to generate a blastocyst, and the ability to generate a blastocyst.
  • Genetics. Chromosomal constitution.
  • Competence, capacity to implant.  

When should we indicate PGT?

 The Preimplantation Genetic Test or PGT is especially indicated if the maternal age is advanced, since both the number of blastocysts and their euploidy (containing 46 normal chromosomes) depend on age.

In a young woman 40% of mature oocytes reach the blastocyst stage, and in older women 30%. After transferring a single blastocyst, the probability of a child being born is three times higher in young women than in older women, due to the fact that the expectation of euploidy is totally different.

The scientific community advises PGT in women over 38 years of age, its indication in women between 35-38 years of age is not so clear, and it is believed that it does not provide a clear benefit in women under 35 years of age, although young women with many embryos could benefit by avoiding the transfer of aneuploid embryos. For women receiving donated eggs, a recent study (1) with more than 1000 patients showed that PGT did not improve outcomes.

PGT is also indicated in cases of:

  • Repeated miscarriage
  • Implantation failure
  • Severe male factor
  • Couples with any type of genetic disorder
  • Previous child with a chromosomal disorder

When is the embryo biopsy performed?

The first embryo biopsies for genetic studies were performed on day 3, at the 8-cell stage, eliminating a blastomere (cell with a nucleus in which the genetic information is found) for study.

 To understand the relevance of this, it is important to know that the embryo is formed by a set of blastomeres and thanks to the studies of Richard Scott’s group (2) we know that eliminating a blastomere decreases the potential for implantation by 19%, which is why this practice is no longer used today.

 Currently, biopsy is performed at the blastocyst stage by obtaining 5-8 cells from the trophectoderm in an embryo that already has between 150-200 cells. Performing the biopsy at the right time (expanded blastocyst) and obtaining the right number of cells does not affect the implantation capacity of the embryo.

 What are the advantages of the PGT?

 The purpose of PGT is not to transfer embryos that will not implant or that if they do implant will end in miscarriage.

 It therefore provides us with information for better embryo selection, but we would like to clarify that it does not increase the efficacy of the treatment; euploid embryos are not created, but they are selected.

 A prospective multicenter study was published this year (3), in which a total of 484 women were transferred a single blastocyst that had been biopsied but without knowing the result of the genetic study carried out. Women who had a euploid embryo transferred had a 65% rate of a child born and those who had an aneuploid embryo transferred had a clinical gestation of 24%, but all ended in miscarriage, the rate of a child at home was 0%.

 The Preimplantation Genetic Test will allow us to shorten the time to achieve gestation and significantly reduce the miscarriage rate. This is of vital importance in older women, as they have a higher percentage of aneuploid embryos.

It is highly recommended to perform PGT-A in this group of women, especially now that it is not so expensive. To understand the importance of this preimplantational test, a 40-year-old woman who receives a blastocyst without genetic diagnosis has a birth rate of 10% but a miscarriage rate of 45-50%.

 Another important benefit is that it allows us to transfer a single embryo, avoiding multiple gestations with a greater number of obstetric complications.

 Future of embryonic genetic diagnosis techniques.

 We have the possibility of analysing DNA present in the culture medium (non-invasively) and thus establish the prioritisation of embryos with a greater probability of being euploid, thus shortening the time to gestation and reducing the abortion rate.

The concordance with invasive methods is over 80%. It is a reproducible, standardised and easy to perform method. It is likely that in the future its combination with other parameters: omics, morphokinetics, etc. will allow us to carry out highly reliable non-invasive studies.

At Clínica Fertia we will continue to train and study all the methods that help us to make our patients’ dreams come true, that is our main commitment.

Would you like to know more about Preimplantation Genetic Testing (PGT)? We encourage you to make an appointment at our fertility clinic so that we can explain it to you in detail and answer all your questions.

Written by:

Dr. Elena Puente

Medical director of Clinica Fertia


More post by Dra. Elena Puente >


  1. Donor oocyte recipients do not benefit from preimplantation genetic testing for aneuploidy to improve pregnancy outcomes. Doyle N, Gainty M, Eubanks A, Doyle J, Hayes H, et al. Hum Reprod 2020;35:2548-55.
  2. Cleavage stage biopsy significantly impairs human embrionic implantation potential while blastocyst biopsy does not: a randomized and paired clinical trial. Scott Rt Jr, Upham KM, Forma EJ, Zhao T, Treff NR. Fertil Steril.2013;100:624-30.
  3. A multicenter, prospective, blinded, non selection study evaluating the predictive value or fan aneuploid diagnosis using a treated next generation sequencing based preimplantation gentic testing for aneuploidy assay and impact of biopsy.Tiegs AW;Zhang Y,Whitehead C,Kim J,Hansan B,et al. Fertil Steril.2021;115:627-37.
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