Understanding the Results of Preimplantation Genetic Diagnosis

By MD, PhD (gynecologist), BSc, MSc (embryologist), BSc, MSc (embryologist), BSc, PhD (senior embryologist), BSc, MSc (embryologist) and (invitra staff).
Last Update: 11/18/2020

The preimplantation genetic test (PGT), formerly known as preimplantation genetic diagnosis (PGD), is a genetic analysis performed on embryos during in vitro fertilization (IVF) treatment.

Its objective is to discard embryos with alterations in their DNA in order to transfer only those that are genetically viable. This allows you to increase the chance of pregnancy and having a healthy baby.

The latest statistics published by the Spanish Fertility Society (SEF) show that the probability of obtaining a positive result in an IVF cycle is greater when embryos are genetically selected (National Registry of Activity 2018-SEF Registry).

Results of PGT

Once the embryonic biopsy has been performed and one or more cells have been sent for analysis, the results of the PGT may take several days depending on the laboratory where it is performed.

During this time, the embryos may remain in culture until they develop to the blastocyst stage or be frozen pending diagnosis.

After obtaining the PGT result report, the embryologist may encounter the following situations:

Healthy embryo
both the number and structure of the embryo's chromosomes are normal. This embryo can be transferred.
Sick embryo
the embryo has some aneuploidy or genetic mutation. This embryo cannot be transferred.
Mosaic Embryo
the embryo has some healthy cells and some sick cells. Depending on the degree of mosaicism and the number of healthy embryos available, the doctor will assess whether to transfer this embryo or not.
Non-informative embryo
there was a failure in the genetic analysis and the embryo could not be tested. You don't know if he's healthy or sick. The doctor will have to assess whether to transfer this embryo or not depending on the number of healthy embryos available.

The percentage of healthy embryos after PGT will depend on the specific genetic alteration and the type of inheritance in case of a hereditary disease.

Depending on the number of healthy or possibly viable embryos (mosaic and non-informative), the decision will be made to how many embryos to transfer to achieve pregnancy. If there are more healthy embryos left over, they will be vitrified for future attempts.

Involved factors

The probability of obtaining a positive IVF-PGT cycle, i.e. a positive genetic test result and a viable pregnancy after the embryo transfer, will depend on the following factors:

  • Experience of the embryologist to perform the embryo biopsy.
  • Number of cells analyzed. With blastocyst biopsy, a greater number of cells are obtained for analysis and the reliability of the result is greater.
  • Technique used to analyze the genetic material of the biopsied cells. Mass sequencing is the most reliable technique today.
  • Quality of tested embryos. Better quality embryos have a higher survival rate.
  • Ability of the embryos to recover from the biopsy. Embryos in the blastocyst stage have a greater capacity for recovery because they have a greater number of cells.
  • Transfer of fresh or vitrified embryos.
  • In the case of hereditary genetic diseases, the probability of obtaining genetically healthy embryos will depend on the type of inheritance: dominant or recessive.

Finally, as in all other assisted reproduction techniques, the most important factor that will determine the success of the treatment is the age of the woman.

Younger women are more likely to obtain genetically normal embryos.

Statistics of PGT

PGT is a complementary technique that is being used more and more routinely in all IVF laboratories.

In 2018, 12,533 IVF cycles were initiated for PGT in Spain, 3,265 more than in 2017.

Indications

Not all couples undergoing in vitro fertilization use PGT. The increase in pregnancy and delivery rates is most evident in those couples with an indication. In 2018, the main causes of indication of IVF with PGT were from more to less:

  • Advanced maternal age (57%)
  • Recurrent miscarriage (8,2%)
  • Molecular diseases (7.2%)
  • Cytogenetic diseases (7.4%)
  • Implantation failures (7.3%)

Therefore, 64.4% of the IVF cycles with PGT performed, more than half, were due to advanced maternal age and the presence of chromosomal abnormalities. The remaining 12.9% is due to other causes.

PGT success rates

There are many ways to represent the success rates of fertility treatments.

Below, we will explain what we consider to be the most important ones based on the latest results of the SEF 2018:

Pregnancy rate
48.8% (pregnancies by embryo transfer)
Birth rate
37.4% (pregnancies by embryo transfer)
Single birth rate
95.1% (single births by number of total births)
Twin birth rate
4.8% (twin births by number of total births)
Miscarriage rate
18.3% (miscarriages by number of pregnancies)

These success rates are higher than those obtained for IVF cycles with own eggs without PGT, which have a pregnancy rate of 35.6% and a delivery rate of 25.7% per transfer.

Finally, it is important to bear in mind that obtaining healthy embryos in the PGT does not guarantee 100% that they will implant and give rise to a gestation, since other factors come into play here, such as the thickness of the endometrium, the rate of embryo division, etc.

Advantages and disadvantages of PGT

Although the most successful assisted reproduction treatment available today in egg donation, genetic analysis of embryos has managed to significantly increase the pregnancy rate per transfer.

This has given women of advanced maternal age the opportunity to become pregnant with their own eggs.

In addition, IVF with PGT has made it possible to reduce the number of embryo transfers destined to failure, which is both a psychological and economic advantage. The downside of all this, however, is that it also increases the number of canceled cycles. Approximately one-third of women who undergo IVF with PGT does not get to transfer any embryos due to aneuploid embryo collection.

Dr. Gorka Barrenetxea says:

The stricter the embryo selection, the more likely it is that we will run out of embryos for transfer.

Let's say we have five blastocysts from a 38-year-old woman. Let's say we do a genetic selection and all five embryos are abnormal. Obviously, the day we break that news is bad news. We have five morphologically perfect blastocysts but they are aneuploid, condemned to non-pregnancy or abortion. Being bad news, it is also good news, since we have just saved 5 transfers, from the administrative and psychological point of view.

FAQs from users

How many embryos are transferred after PGD?

By Susana Cortés Gallego BSc, PhD (senior embryologist).

The number of embryos to be transferred to a patient does not depend on the technique that has been practiced on the embryo, but on the day it is found, its quality and the intrinsic characteristics of each patient. The performance of a Preimplantation Genetic Diagnosis is associated in most cases with advanced maternal age (screening of aneuploidies) or the presence of serious genetic pathologies (in many cases present in the woman). In both cases, multiple pregnancy is contraindicated.

For all these circumstances, the medical advice is usually the transfer of a single embryo.

How many eggs must be obtained for the PGD cycle to be successful?

By Sara Salgado BSc, MSc (embryologist).

For there to be a reasonable probability of success in the IVF cycle with PGD, it is important to recover a good number of eggs in the follicular puncture. Generally, obtaining 6 or more eggs would be best. On the other hand, if the woman is a low responder, there is little chance that IVF with PGD will be successful.

There is also the option of making cycles of egg accumulation to obtain several embryos from several cycles and to be able to analyze them all together. In this way, the probability of success is increased and the cost of treatment is reduced.

How long does it take to get the results of PGD?

By Sara Salgado BSc, MSc (embryologist).

From the time the embryonic biopsy is performed and the cells are sent for analysis, it usually takes about 48 hours until the result is received and the woman or couple is notified.

However, this depends on the clinic and the laboratory making the diagnosis. On occasion, the results may take a week, so it will be necessary to vitrify the embryos in order to transfer them in a next cycle.

Suggested for you

If you do not know what the whole IVF procedure with PGT consists of, do not miss the explanation in the following post: What is the preimplantation genetic test or PGT?

For more information on the probability of getting pregnant through fertility treatments, you can read on here: Success rates of fertility treatments.

Our editors have made great efforts to create this content for you. By sharing this post, you are helping us to keep ourselves motivated to work even harder.

References

Authors and contributors

 Gorka Barrenetxea Ziarrusta
Gorka Barrenetxea Ziarrusta
MD, PhD
Gynecologist
Bachelor's Degree in Medicine & Surgery from the University of Navarra, with specialty in Obstetrics and Gynecology from the University of the Basque Country. He has over 30 years of experience in the field and works as a Titular Professor at the University of the Basque Country and the Master's Degree in Human Reproduction of the Complutense University of Madrid. Vice-president of the SEF. More information about Gorka Barrenetxea Ziarrusta
License: 484806591
 Neus Ferrando Gilabert
Neus Ferrando Gilabert
BSc, MSc
Embryologist
Bachelor's Degree in Biology from the University of Valencia (UV). Postgraduate Course in Biotechnology of Human Assisted Reproduction from the Miguel Hernández University of Elche (UMH). Experience managing Embryology and Andrology Labs at Centro Médico Manzanera (Logroño, Spain). More information about Neus Ferrando Gilabert
 Sara Salgado
Sara Salgado
BSc, MSc
Embryologist
Degree in Biochemistry and Molecular Biology from the University of the Basque Country (UPV/EHU). Master's Degree in Human Assisted Reproduction from the Complutense University of Madrid (UCM). Certificate of University Expert in Genetic Diagnosis Techniques from the University of Valencia (UV). More information about Sara Salgado
 Susana Cortés Gallego
Susana Cortés Gallego
BSc, PhD
Senior Embryologist
Bachelor's Degree in Biological Sciences from the Complutense University of Madrid, and PhD in Comparative Animal Physiology from the Faculty of Biological Sciences. Extensive experience in the scientific field, and currently working as the coordinator of the laboratories of Clínica Tambre in Madrid, Spain. More information about Susana Cortés Gallego
License: 17980-M
 Zaira Salvador
Zaira Salvador
BSc, MSc
Embryologist
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV
Adapted into english by:
 Romina Packan
Romina Packan
inviTRA Staff
Editor and translator for the English and German edition of inviTRA. More information about Romina Packan

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