Category
Dec 4, 2025
Sometimes, everything looks perfect. The embryo appears ideal under the microscope, the uterus is ready... and yet, the pregnancy test is negative or, even more painfully, the pregnancy stops after a few weeks. Why does this happen?
The answer is often invisible to the human eye: genetics.
At Institut Marquès, we understand that your goal is not just "to get pregnant," but to bring a healthy baby home. That is why genetics is not a luxury; it is our most powerful tool to save you time, money, and emotional suffering. In this article, we translate complex science so you understand how we "read" the future of your embryos.
Before looking at the embryos, we must look at those who create them: you and your partner.
What is the Karyotype? The karyotype is a simple blood test that analyzes the chromosomes of the prospective parents. It allows us to "read their genetic map" to confirm if they have the correct number of chromosomes (46) and if they are ordered properly.
Why is it the first step? Sometimes, a perfectly healthy person may have a small alteration in their chromosomes (such as a "translocation" or "inversion"). It does not affect them, but when transmitting that genetic instruction to the embryo, it can cause sterility or recurrent miscarriages. If we detect this, we know we will need the help of PGT.
This is the revolution of modern reproductive medicine. We no longer choose embryos just for "being pretty," but for being healthy.
Definition: PGT PGT (formerly called PGD) is an advanced technique that allows us to analyze the genetics of the embryo before transferring it to the uterus. Through a painless biopsy for the embryo, we study its DNA to discard those with anomalies and select only those capable of resulting in a healthy baby.
Who needs it most? Biology is clear: from age 35-38, egg quality decreases, and the risk of genetic errors increases. PGT is the "filter" that allows us to overcome this age barrier.
When we analyze an embryo using PGT-A (the most common type), we look for "accounting" errors in the chromosomes.
What is an Aneuploidy? An aneuploidy is an alteration in the number of chromosomes. A healthy embryo (euploid) must have 46 chromosomes. If it has one too many (as in Down Syndrome) or one too few, it is considered aneuploid.
The reality that protects: Most aneuploid embryos never implant or end in miscarriage. By identifying them in the laboratory and not transferring them, we are protecting you from a failed treatment and bringing you closer to a real pregnancy.
Genetics is not always "black or white." Sometimes, we find a gray area.
Definition: Embryonic Mosaicism We speak of mosaicism when an embryo has a mixture of cells: some are genetically normal and others abnormal.
Can they be transferred? Yes, under expert advice. Not all mosaic embryos are discarded. Some have the amazing ability to "self-correct" and result in a perfectly healthy baby. At Institut Marquès, our genetic committee evaluates each case so as not to waste any opportunity for life.
If there is a known serious disease in your family (such as Cystic Fibrosis, Huntington's, or Thalassemia), our goal changes. We do not look for random errors; we look for a specific footprint.
What is PGT-M? It is the Genetic Test for Monogenic diseases. It allows us to identify with precision which embryos have inherited the disease from the parents and select for transfer only those free of the pathology. It is the definitive tool to break the chain of transmission of a hereditary disease.
Does the biopsy damage the embryo? It is the most common fear, but the answer is reassuring. The biopsy is performed on Day 5 (blastocyst), extracting with a laser a few cells from the outer layer (trophectoderm, which will form the placenta), never touching the inner cell mass (which will form the baby). In the hands of our experts, the risk of damage is less than 1%.
Does PGT guarantee pregnancy 100%? There is no 100% in medicine, but PGT drastically increases the pregnancy rate per transfer. By transferring only healthy embryos (euploids), we avoid "spending" time and hope on embryos that would never have worked.
If I am young, do I need PGT? It is not always necessary on the first attempt. However, if you have suffered previous miscarriages or unexplained implantation failures, PGT can give us the answer you are looking for, regardless of your age.
