PRE-IMPLANTATION GENETIC SCREENING OF THE CHROMOSOMAL ANEUPLOIDIES (PGS)
ANALYSIS OF THE CHROMOSOMAL ANEUPLOIDIES
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A recognised cause of infertility is the production of embryos with an aneuploid chromosal structure, that is, with anomalies at the level of the number of chromosomes
This phenomenon is mainly found in women of a certain age (≥ 36 years). Most of the aneuploidies found in the embryo are of maternal origin and originate from the two meiotic divisions of the oocyte during its maturation.
In couples who are following an assisted reproduction programme (MAP), it is now possible to control the embryos before transferring them into the uterus, thus reducing the risk of transferring any aneuploid embryos. In addition to the increase in the pregnancy rate, the benefits include a reduction in the number of spontaneous abortions and any chromosomal abnormalities detected during prenatal analysis.
WHICH CELLS ARE ANALYSED
In line with the latest international recommendations, the Centre proposes two types of embryonic biopsy:
► Analysis of the polar globules of the oocyte
► Analysis of the trophectoderm cells of the blastocysts
Biopsy of the polar globules of the oocyte
This allows for determining the chromosomal structure of the oocyte. It is a technique indicated when the causes of infertility are mainly linked to the maternal age (≥ 36 years).
Trophectoderm cells (TE) of the blastocysts
This allows for analysing the genetic material from both partners.
Each of these two possibilities offers the advantage and the selection of the type of biopsy to carry out depending on the specific problems of the couple. The choice is made together with the doctor who will know how to advise the best method to undertake.
WHAT ARE TROPHECTODERM CELLS
Trophectoderm cells are the ones that make up the outer layer of the blasocysts. At this stage, the embryo consists of a few hundred cells. The trophectoderm forms the placenta while the embryo will be formed by the internal mass. The biopsy of several cells for the genetic analysis is carried out on the trophectoderm. In this way, the internal mass that will form the embryo will not be touched.
WHAT ARE POLAR GLOBULES
Polar globules are produced during the maturation of the oocyte and contain the supplementary chromosomal structure of the oocyte. They do not serve any purpose and are not future constituents of the embryo but instead represent a so-called “derivative product” that can be extracted for the genetic analysis. In this way, the embryo is not touched or damaged.
THE PGS PROCEDURE
The polar globules or trophectoderm cells are delicately detached from the oocytes and blastocysts respectively using a laser beam. This is a very precise technique that allows for recovering several cells without damaging the oocyte or embryo.
The genetic material is then analysed by means of a very novel technique called Next Generation Sequencing (NGS) which makes it possible to analyse all the chromosomes both in terms of their number and for any subtle abnormalities inside them. The NGS technique is also indicated for detecting the presence of any mosaicism in the trophectoderm cells.
WHO IS THE TEST CONDUCTED ON?
The Pre-implantation Genetic Screening (PGS) is conducted on the following categories of patients:
Maternal patients of a certain age
Patients aged 36 years or over, especially if they produce a high number of oocytes after ovarian stimulation (> 8 oocytes). Numerous studies have shown that in women over the age of 38, aneuploid embryos (with an abnormal chromosome number) range from 63% to more than 80% at a more advanced reproductive age. The number of oocytes with numerical chromosomal abnormalities already increases exponentially after the age of 36 years.
After several failed MAP attempts
Patients with 3 or more failed attempts at IFV-ET or ICSI cycles (due to lack of pregnancy or repeated abortions) after excluding other causes, such as autoimmunity, thrombophilia, endometriosis, female genital system malformations, chromosomal translocations, etc.
Balanced translocations in one of the two partners.
Couples with a balanced chromosomal translocation often encounter the inability to generate a pregnancy and/or have recurrent spontaneous abortions due to the production of embryos with an unbalanced chromosome structure. The technique only allows embryos with a normal or balanced chromosome structure to be selected. This greatly reduces the risk of an interrupted pregnancy.
THE SUCCESS RATE
The chances of success in terms of a term pregnancy depend on many factors, some easily diagnosable, others still unknown. Procrea has been operating for years in the sector of medical genetics in the aim of providing more accurate diagnoses and targeted treatments.
While PGS is not able to guarantee success, it certainly contributes towards increasing the probabilities.
In women over the age of 40, the success of the transfer ranges from 17% to more than 40%.
THE QUALITY OF THE ANALYSIS
The genetic analysis of a single cell is an extremely sophisticated procedure that requires highly qualified staff and an adequate infrastructure. Our laboratory is certified and accredited with international standards in this sector (ISO/IEC 17025 and ISO 15189). This accreditation ensures the highest quality standards and the probability of errors reduced to a minimum.