Everything You Need to Know About Embryos and Their Possible Aneuploidies Before You Embark on Your Fertility Treatment

While most people are aware that, in terms of assisted reproduction, an embryo represents the initial stage of development of a human being, they may not be as familiar with the other concept in the spotlight today: aneuploidy. Aneuploidies are defined in this context as chromosomal alterations that embryos can present, which can lead to genetic diseases in future offspring and even be incompatible with life.

IVF-Life’s track record, the techniques we use and the experience and protocols that characterise our specialists are the factors that will make it possible to diagnose these anomalies and, consequently, prevent them from occurring.

What are Embryonic Aneuploidies? Definition and Examples

As was just mentioned, aneuploid embryos are those that harbour certain variations in their genetic content that make them unsuitable for transfer to the patient’s uterus. The karyotype of a person, or, in other words, the set of chromosomes that each person possesses, is made up of 23 pairs of chromosomes, 22 of which are named autosomal and the remaining pair corresponds to the so-called sex chromosomes (XX in the case of women and XY in the case of men).

One of the most common examples of aneuploidy detected in embryos regarding the number of autosomal chromosomes is Down’s syndrome, which involves a trisomy of chromosome 21 (having three copies of chromosome 21 instead of two). While people with this condition currently have a life expectancy of up to 65 years, according to experts in the field, others do not have the same prognosis. Other common trisomies are Edwards’ syndrome (presence of an extra chromosome 18) and Patau syndrome (trisomy of chromosome 13), where in both cases the newborn usually passes before reaching their first year of life.

On the other hand, aneuploidies linked to the sex chromosomes include Klinefelter syndrome, which occurs in males with an extra X chromosome, and XYY or Jacobs syndrome, characterised by the possession of an extra Y chromosome and also occurring in males. On the other hand, females can be affected by Turner syndrome (missing X chromosome) and triple X syndrome or trisomy X, which, as the name suggests, is associated with having an extra X chromosome.

Causes of Aneuploidy in Embryos

Numerous investigations have been carried out over the years regarding this matter, with the aim of finding out what factors trigger the appearance of aneuploidy. The reason most supported by experts is linked to the production of the gametes – eggs and spermatozoa – also being particularly relevant the extent to which ovogenesis is influenced by the woman’s age.

As is well known, the older a woman is, the more difficult it becomes to achieve a pregnancy that does not lead to complications and that is successfully carried to term. Similarly, the rate of embryonic aneuploidy increases considerably, especially after the age of 39, when almost 50% of the embryos that are generated have some kind of anomaly. Although a small percentage of these may have the capacity to implant, it is common for them to end up leading to miscarriage and, if this does not occur, the baby will be born with the corresponding alteration. Due to this reason, specialists in reproductive medicine always recommend the use of aneuploidy diagnosis techniques in order to guarantee a simpler, more pleasant process, which also will not take too long.

How Are Embryonic Aneuploidies Diagnosed?

Assisted reproduction offers experts and their patients the option of detecting aneuploidy in embryos through one of the techniques included in the so-called Preimplantation Genetic Testing, specifically PGT-A (Preimplantation Genetic Testing for Aneuploidy).

In order to carry it out, it is necessary to perform a biopsy of the trophectoderm cells of the embryos generated in an In vitro fertilisation treatment, when these are at day 5 of their development, that is, in the blastocyst stage. By analysing this sample, the specialised laboratory will provide information on the chromosomal content of the embryo and its viability before the transfer stage is reached. There are 3 possible results that can be obtained following PGT-A, all of which are detailed below.

Aneuploid Embryos and Euploid Embryos

As explained throughout the article, aneuploid embryos are those whose content shows some alteration in the number of autosomal or sex chromosomes, either a loss or a gain, and are therefore considered unsuitable for embryo transfer. Conversely, euploid embryos are those containing 23 pairs of chromosomes and are those that are transferred to the maternal uterus or cryopreserved for this purpose in future cycles.

Mosaic Embryos

In addition to those mentioned above, there is another type of result that can be obtained and that is embryonic mosaicism. This means that there are two types of cells in the embryo, some with abnormalities and others that are chromosomally “normal”. These are not usually embryos that are chosen for transfer, but it is possible to choose to transfer them if there are no euploid embryos at all in the chamber. This decision should only be made with the authorisation of the relevant specialists and after the woman or couple has been fully informed of the associated risks.

Other Tests to Detect Aneuploidy

Many patients ask whether aneuploid embryos can be identified in another way, for instance, by studying their quality, and the answer to this is a resounding no, because even if an embryo is morphologically optimal, it can still harbour chromosomal abnormalities.

People who have not opted to undergo Preimplantation Genetic Testing in their assisted reproduction process or who need confirmation that everything is going as expected, can also resort to prenatal testing. NIPT (non-invasive prenatal screening) can detect aneuploidies in the foetus through blood testing of the mother from the ninth week of gestation onwards. Later in pregnancy, invasive prenatal tests such as chorionic villus sampling (CVS) or amniocentesis can also be employed, which, although they may be more reliable, carry a small risk of gestational loss.

PGT-A is the perfect tool to find out about the aneuploidy of embryos when planning a pregnancy and, therefore, at IVF-Life we recommend that all our patients incorporate this technique into the treatment they undergo with us. Do you have any further questions about this topic or do you want to know how everything we just explained applies to your personal case? In our fertility clinics in Alicante, Donostia and Madrid we have everything you need to ensure that your treatment is suitable for you and that your pregnancy will become a reality.