A known cause for infertility is the production of embryos with a chromosomal aneuploid asset, i.e. with abnormalities in the number of chromosomes. This issue is primarily found in women at an advanced reproductive age (>36 years). The majority of aneuploidies found in the embryo are of maternal origin and stem from two meiotic divisions of the oocyte occurring during maturation.

It is possible to check, in a couple who undergoes a programme of assisted reproduction, the polar cells of the fertilised oocytes before implanting the embryos in the body of the woman, thus reducing the risk of transferring an aneuploid embryo while also increasing the probabilities of a pregnancy.

WHAT ARE THE POLAR CELLS?

The first polar cell is produced during the first division of the oocyte and contains half of the chromosomal asset of the oocyte (23 chromosomes). After the second division of the oocyte, the second polar cell is expelled. These cells do not have any function and will not be part of the embryo, they are the so-called “by-products” and can be removed to be analysed and determine if the oocyte contains the correct number of chromosomes (23). This way, the embryo is not touched and/or damaged. 

HOW IS POLAR CELL ANALYSIS CARRIED OUT? 

The polar cells are extracted after making a small hole in the zona pellucida, using a laser beam. The genetic material is then analysed through a very sensitive technique called Array-CGH. This technique allows for an analysis of all chromosomes as regards their number and any subtle abnormalities inside them. After removing the polar cells, an intra-cytoplasmic sperm injection (ICSI) is performed. 

FOR WHOM IS THIS TEST INTENDED?

The pre-implant genetic screening (PGS) is intended for the following categories of patients:

Advanced maternal age

Patients aged 38+ years, especially if they produce a high number of oocytes after ovarian stimulation (>8 oocytes). In fact, the test allows avoiding the freezing of the aneuploid zygotes and their transfer during the following cycles, thus causing a waste of time which is essential after 36 years of age, as well as the repetition of a quite costly treatment (defreezing and transfer). Numerous studies have in fact demonstrated that in women aged 38+ years, the aneuploid embryos (with an abnormal number of chromosomes) range from 63% to more than 80% in an advanced reproductive age.

After several failed PMA attempts

Patients with 3 or more failed FIVET or ICSI cycle attempts (because of non-pregnancy or repeated miscarriages), once other causes are excluded, e.g. autoimmunity, thrombophilia, endometriosis, malformations of the female genital apparatus, chromosomal translocation in the partner, etc.

Maternal balanced translocations

Patients with a balanced chromosomal translocation often face the incapacity to generate a pregnancy and/or recurrent miscarriages due to the production of oocytes with an unbalanced chromosomal asset. This technique allows the selection only of the oocytes with a normal or balanced chromosomal asset.

PERCENTAGE OF SUCCESS 

The probabilities of success, in terms of a pregnancy carried to term, depend on many factors such as the maternal age and the quality of the embryos. The PGS cannot ensure success, but it certainly contributes to an increase in its probability. In women above 40 years of age, the percentage of transfer success increases from 17% to more than 40%.