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When a fertilization process takes place, where the egg and sperm unite, the development of the embryo begins. At that moment, the egg and sperm perform their function of chromosomal contribution. Each of them provides 23 chromosomes, forming the 46 that a human typically presents.
However, sometimes the number of chromosomes is altered. When this happens, it is called an aneuploid embryo. This is more common than we might think, as one in three embryos shows aneuploidies originating during the formation of gametes or after fertilization, and it is more frequent in eggs than in sperm or most somatic cells.
This variation can cause genetic diseases or even be incompatible with life. It is also a direct cause of infertility, spontaneous miscarriages, or congenital syndromes.
Difference between embryonic aneuploidy and mosaicism
When mentioning aneuploidy, the term is often confused with mosaicism. Although they have similar meanings, their conditions are different. Therefore, it is essential to understand the nature of each.
As we have seen, aneuploidy refers to an embryo where all —or most— of its cells have an abnormal number of chromosomes (above or below 46), while mosaicism is a condition in which the embryo contains a mixture of chromosomally normal (euploid) and chromosomally abnormal (aneuploid) cells.
Why do these chromosomal alterations occur?
Scientific research and studies have confirmed that the woman’s age is the most common reason why these chromosomal alterations may appear. The older the woman is, besides having more difficulties achieving pregnancy, the higher the chances of causing or developing embryonic aneuploidy.
From the age of 39, it is considered that 50% of embryos generated present some kind of anomaly.
Euploid Embryo
Mosaic Embryo
Aneuploid Embryo
Euploid Cell
Normal Number of Chromosomes
Euploid and Aneuploid Cells
Healthy (Euploid) Cells Coexist with Altered (Aneuploid) Cells
Aneuploid Cell
Abnormal Number of Chromosomes
What role does assisted reproduction play?
Assisted reproduction plays an essential role when it comes to embryonic aneuploidy. The high qualification of embryologists, together with advanced reproductive medicine techniques, ensures the viability of healthy embryos, thus discarding those that carry any anomaly.
PGT-A:
PGT is a technique that prevents the transfer of embryos with chromosomal and/or genetic alterations to the uterus, which could lead to recurrent miscarriages or the birth of babies with severe diseases.
When this technique is used to identify and discard aneuploid embryos, it is called PGT-A. This technique is applied during assisted reproduction treatments, usually when the embryos have been cultured for 5 days and have reached the blastocyst stage, at which point an embryo biopsy is performed.
Safety and peace of mind for the patient
All these advances applied in assisted reproduction mean safety and peace of mind for the patient in any of the different treatments.
Moreover, the high success rates confirm that, despite producing embryos with chromosomal alterations, the birth of a healthy baby will occur thanks to the PGT-A technique.
