Pre-implantation genetic testing (PGT) involves specialist genetic investigations of embryos before their transfer to the womb.
Pre-implantation testing is used to prevent congenital genetic disorders in children of couples with genetic risk factors or to increase the chances of having a healthy child by patients without identified familial factors who, for various reasons (age, multiple failures of embryo implantation, multiple miscarriages, a child with aneuploidy), have the embryos tested for the correct number of chromosomes.
Chromosomal abnormalities in embryos are among the main reasons of IVF failures. Each embryo’s cell should contain 46 chromosomes (23 pairs). They are ‘carriers’ of genes and contain information on how the embryo should develop into a healthy child. When a cell contains an extra chromosome or any chromosome is lacking, this is called aneuploidy.
Aneuploid-cell embryos usually fail to implant in the uterus; there are also cases of early miscarriage after implantation. However, few aneuploidies allow pregnancy development until childbirth. The most common defect that does not result in the early embryo’s death is trisomy 21 called Down’s syndrome.
Research shows very frequent chromosomal abnormalities in embryos. The risk of an embryo having the abnormal number of chromosomes depends on the mother’s age. Approximately 25% of about 30-year-old women’s embryos demonstrate chromosomal abnormalities while for women aged about 40 years – more than a half of embryos.
Assisted reproduction technologies do not increase the risk of chromosomal abnormalities. However, only IVF gives us the opportunity of embryo screening to detect aneuploidies before the embryo is transferred to the womb.
PGT-A/PGS is recommended in the case of:
A few cells are removed from the cultured embryos at the cytoblastic stage on Day 5 or Day 6. Genetic material is isolated from the cells and then analysed using the NGS technology. The embryos are frozen and safely stored until the results are obtained. The test cost is provided in the price list.
The test report contains information about the number (correct or not) of chromosomes in the embryo’s cells. When abnormalities are detected, there is information on the affected chromosome and whether all the other cells analysed are defective. Centrum Medyczne Macierzyństwo cooperates with the genetic laboratory www.coopergenomics.com
Diagnostic testing for monogenic disorders is a targeted method to look for a specific genetic alteration – mutation causing a familial disease.
When parents are carriers of a genetic disorder (a monogenic disease), their chance of having healthy children is very small. Pre-implantation screening allows to check embryos for a specific abnormality and to transfer embryos with no mutation. Therefore, even couples without a natural conception problem decide to have PGT-M.
Diagnostic pre-implantation PGT-SR screening is a solution for patients being carriers of balanced translocations. Usually, the status of balanced translocation carrier (i.e. altered arrangements of the genetic material in chromosomes without any size changes) is not associated with any symptoms.
Translocations can be detected using a test called karyotyping. Translocation carriers are at a much higher risk of miscarriage or having a child with unbalanced translocation (i.e. alteration of both genetic material arrangement in chromosomes and of its size, which always results in health problems). PGT-SR for translocations allows transfer of healthy embryos.