An embryo is considered normal when it has 23 pairs of chromosomes, while any numerical type of chromosomal abnormality is called aneuploidy. Aneuploidies are responsible for the largest percentage of miscarriages in the first trimester.
How do aneuploidies occur?
Aneuploidy results from either the fertilization of an abnormal egg or sperm or an error in the mechanism of chromosome segregation during cell division during embryonic development.
What else can cause the creation of a pathological fetus?
Another reason for the creation of abnormal embryos is the balanced chromosomal rearrangements (balanced permutations, inversions) in the karyotype of one or both prospective parents. Chromosomal rearrangements in the fetal karyotype increase the percentage of abnormal fetuses and most often cause miscarriage or pregnancy with a chromosomal abnormality.
How can preimplantation genetic testing for chromosomal and structural chromosomal abnormalities help?
Preimplantation genetic testing for chromosomal abnormalities is recommended in couples undergoing an IVF cycle and aims to analyze the entire genome for chromosomal abnormalities (numerical and structural) in embryos in order to avoid abnormal embryo transfer. The test is performed on the fifth day of their embryonic development in vitro (blastocyst stage). At this stage the biopsy is performed, ie the removal of 5 to 8 cells from a part of the fetus that plays a role only in the formation of the placenta (trophoderm). The biopsy material is analyzed by the genetics department with the NGS method (new generation sequencing). The disadvantage of the test is that it can not control all embryos except those that reach the blastocyst stage and have a good morphology.
When does the embryo transfer take place?
Upon completion of the biopsy procedure, the embryos are frozen to give the laboratory time to complete the genetic analysis. Biopsy and freezing procedures are routine procedures in our laboratory with excellent survival rates. At the end of the examination, the fetuses that will be considered normal are transferred to a next cycle, where the endometrium will be properly prepared to receive it.
What is preimplantation genetic diagnosis?
Preimplantation Genetic Diagnosis (PGD) is applied to the fetuses of couples with a predisposition to the birth of a child with an inherited disease such as Mediterranean anemia and cystic fibrosis. In this case, the couple does not have a fertility problem but undergoes a conventional in vitro fertilization cycle in order to genetically test their embryos and transfer only the healthy ones to the expectant mother’s uterus. The main goal of preimplantation genetic diagnosis is to have a healthy child and to avoid termination of abnormal pregnancies that may result from natural conceptions due to a history of inherited diseases.
What are the latest developments?
The combination of the use of embryoscope technology (high-tech microscope that makes it possible to monitor, record and videotape the development of embryos) and artificial intelligence, as well as the analysis of fetal genetic material by non-invasive procedure (analysis of fetal DNA found in cultivation material) are the future.
Having 35 years of experience in the field of genetics and embryology, it was my honor to be a pioneer in many innovative techniques in Greece and worldwide. Excited and excited, I participate in new developments always with the first thought to help as many couples as possible to achieve the big dream: having a child.
Writes:
Stephen Davies Εμβρυολόγος
Director of Embryological Laboratory HYGEIA IVF Unit Embryogenesis
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