Preimplantation diagnosis consists of genetic testing of embryos before they are transferred into the uterine cavity. Its aim is to reduce the risk of genetic abnormalities in fetuses and children by detecting embryonic aneuploidy (PGS) or specific genetic alterations (PGD), thereby increasing the chance of achieving a pregnancy, reducing the risk of miscarriage, and reducing the risk of multiple pregnancy through single embryo transfer (SET).
For couples entering treatment, preimplantation diagnosis allows for fewer cycles of treatment with in vitro fertilization methods, decreasing the time to achieve pregnancy and reducing treatment costs.
The sensitivity and specificity of preimplantation diagnosis methods is very high, but it does not give 100% certainty of detecting all genetic abnormalities. It is recommended to perform prenatal tests in pregnancies obtained from embryos that have undergone previous genetic testing. Unfortunately, a correct test result does not guarantee the correct course of pregnancy and birth.
What are chromosomal abnormalities?
Chromosome abnormalities in embryos are one of the major causes of IVF treatment failure. Each embryo cell should contain 46 (23 pairs) chromosomes. They are the "carrier" of genes and contain information about how the embryo will develop into a healthy baby. Situations, where a cell has an excess or missing chromosome, are called aneuploidies.
Aneuploid embryos usually do not implant in the uterus at all, and it also happens that if such an embryo does implant, the pregnancy ends in an early miscarriage. However, few aneuploidies allow the pregnancy to progress until the baby is born. The most common aneuploidy that does not cause the embryo to die at an early stage of its development is trisomy 21 chromosome - Down syndrome.
How common are aneuploidies in embryos?
Studies show that chromosome abnormalities in embryos are very common. The risk of having an embryo with an abnormal number of chromosomes depends on the age of the mother. In women who are approx. 30 years of age, about ¼ of the embryos show chromosome abnormalities. The use of assisted reproduction methods does not increase the risk of chromosomal abnormalities. But only with the use of in vitro methods are we able to carry out embryo screening, i.e. to detect aneuploidies even before the embryo is implanted in the uterus.
When to consider genetic screening?
Use of the PGT-A/PGS method is recommended for:
Women over 35
Abnormal karyotype of either parent after genetic counselling
Prior birth of a child with trisomy
Particular fear of having a baby with trisomy (Down syndrome, Edwards syndrome, Patau syndrome)
How is embryo screening performed?
In ⅚ days of culture, several cells are collected from embryos that are at the blastocyst stage. Genetic material is isolated from the cells, which is then analyzed by NGS. The embryos are frozen and stored safely until the result is received. The cost of the test can be found in the price list of the clinic you're attending.
The test result indicates whether the correct number of chromosomes was found in the germ cells examined. If abnormalities are detected, information is given on which chromosome is affected and whether they were found in all the embryo cells analysed. The Macierzyństwo Medical Centre cooperates with the genetic laboratory www.coopergenomics.com.
Diagnosis for single-gene diseases is a directional test that looks for a specific genetic change - a disease-causing mutation that runs in a family.
When the parents are carriers of a genetic abnormality (monogenic diseases), their chance of having healthy offspring is very limited. Preimplantation diagnosis makes it possible to check embryos for the abnormality in question and to only implant embryos that are not affected by the mutation during embryo transfer. In this situation, even couples who have no problem getting pregnant naturally decide to use PGT-M.
PGT-SR preimplantation diagnosis is an option for patients who are carriers of a balanced translocation. Carrying a balanced translocation (a change in the arrangement of genetic material in the chromosomes, without a change in the amount of material) is usually asymptomatic and can be detected by karyotype testing. Carrying a translocation significantly increases the risk of losing a pregnancy or having a baby with an unbalanced translocation (i.e. a change in both the arrangement and amount of material in the chromosomes, which always has health consequences). Performing PGT-SR testing for translocations allows for uncharged embryos to be given during embryo transfer.