6 de June, 2023

Aneuploidy: What it is, causes and how to prevent it

Aneuploidy is the presence of an abnormal number of chromosomes, a genetic alteration that can occur in the embryo and compromise the term of a pregnancy. Below, we explain what causes it and how you can prevent this type of condition.

Aneuploidy, what is it?

Each of the tissues and organs that make up the human body are made up of somatic cells, which in turn are derived from stem cells that originate during embryonic development.

Human somatic cells are diploid, which means that they normally have 23 pairs of chromosomes (46 chromosomes in total), in which all the genes are distributed and which are responsible for storing genetic information. Sex cells (eggs and sperm), on the other hand, are haploid and contain only half as many chromosomes.

A cell containing a normal chromosome load is known as euploid, but when a cell has an abnormal number of chromosomes (either more or fewer), it is referred to as aneuploid.

If the abnormal number results in fewer than 46 chromosomes, this is known as monosomy, whereas if there are more chromosomes, it is known as trisomy.

What are the causes of aneuplodies?

Most of the alterations that cause chromosomal gains or losses originate during a process called gametogenesis, which refers to the process in which the gametes, i.e. the egg and sperm, are formed.

It mainly occurs during the ovogenesis or development of the egg cell (during meiosis I), while another considerable percentage of these alterations arise during early mitosis (a process occurring in the nucleus of eukaryotic cells, prior to cell division, which consists of the equal distribution of hereditary material), after fertilization.

Around 50% of all embryos that are produced by assisted reproduction techniques are aneuploid, the rate of aneuploidy increases as maternal age increases. A higher percentage of aneuploid embryos is produced after 37 years of age.

The trisomies most frequently found in embryos via IVF are 16, 19 and 21 (chromosomes) while monosomy 22 and partial loss of the Y chromosome are the most frequent monosomies.

All monosomies (except for monosomy X or Turner syndrome) are incompatible with life, i.e. embryos with this alteration cannot develop.

In contrast, all trisomies can result in a baby with serious health problems. The type of involvement, phenotypic characteristics and life expectancy of that baby will depend on the type of trisomy present.


Trisomy 21, for example, is a disorder that gives rise to Down's syndrome, and is one of the most common trisomies (1 case in 700). This condition is also characterized by the fact that people tend to:

  • Being prone to congenital heart disease.
  • Mental retardation of varying degrees.
  • Have an average life expectancy of 50 years.

How do aneuploidies impact your reproductive health?

About 35% of all implantation failures that occur in Assisted Reproduction treatments, which is one of the main causes of infertility, are due to the transfer of aneuploid embryos.

In case you are over 37 years old and are undergoing a process of Assisted Reproduction, or are considering starting this path, you should know that there are alternatives to prevent the embryos from presenting aneuploidies and other types of genetic alterations, so that you can have a baby at home, and this will have the best possible quality of life.

You can achieve your baby without this disturbance being an obstacle.

To prevent genetic alterations such as aneuploidy from affecting the embryos, your specialists may recommend and carry out a test called Prenatal or Preimplantational Genetic Diagnosis (PGT).

This analysis is performed on all embryos generated by IVF in order to know their chromosomal profile, and thus avoid the transfer of aneuploid embryos to the uterus. This will increase the chances of implantation, pregnancy and having a baby at home.


PGT is usually recommended for patients undergoing assisted reproduction treatment if:

  • The woman is over 37 years old.
  • The male or female has a family history of aneuploidy.
  • Implantation failure occurs.
  • Recurrent miscarriages have occurred.

If this is your case or if you want to know more about PGT testing to minimise the risk of your baby having conditions that compromise their quality of life, we invite you to visit our page on Preimplantation Genetic Diagnosis.


  1. Hassold, T. and Hunt, P. To err (meiotically) is human: the genesis of human aneuploidy. (2001). Nature reviews Genetics.
  2. Ramia, M., Musharrafieh, U., Khaddage and W., and Sabri, A. Revisiting Down syndrome from the ENT perspective: review of literature and recommendations . (2014). European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies.
  3. Rubio, C., Bellver, J., Rodrigo, L., Castillon, G., Guillen, A., Vidal, C., Giles, J., Ferrando, M., Cabanillas, S., Remohi, J., et al. In vitro fertilization with preimplantation genetic diagnosis for aneuploidies in advanced maternal age: a randomized, controlled study.. (2017). Fertility and sterility.

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