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Preimplantation Genetic Diagnostics
The use of preimplantation genetic diagnostics is possible only with IVF program, and at one time it became a real breakthrough in the field of assisted reproductive technologies. The ability to detect genetic disorders at the stage of pre-implantation development is a chance to significantly increase the effectiveness of infertility treatment and achieve the main goal – the birth of a healthy baby in the family.
Preimplantation genetic screening of an embryo for chromosomal abnormalities allows selecting healthy embryos with a normal number of chromosomes (euploid). Embryos with the wrong number of chromosomes (aneuploid) are either not viable, or carry the risk of giving birth to a child with a genetic pathology, including down syndrome, malformations of various organs and systems. Transferring an embryo with a normal number of chromosomes significantly increases the effectiveness of the IVF program, reduces the number of unsuccessful attempts, and reduces the risk of miscarriage.
In addition, PGD is the only method of preventing the transmission of monogenic diseases in the family. Preimplantation diagnostics technology minimizes the risk of having a child with a pathology in spouses who are carriers of a hereditary monogenic disease (a defective gene).
What is an embryo’s PGD?
Pre-implantation Genetic diagnosis (PGD) is a method that allows you to make a genetic diagnosis of an embryo before the procedure of in vitro fertilization (IVF). The task of diagnostics is to provide an opportunity to give birth to healthy children in families where there is a high risk (high probability) of having a child with severe genetic diseases.
There are 3 indicators that the PGD can tell you about.
The first is an assessment of the number and quality of chromosomes in the embryo, in other words, an assessment of the chromosomal status. All the inherited information in each cell is contained in the DNA, which is Packed in 46 chromosomes. PGD allows you to exclude or confirm the presence of chromosomal abnormalities, such as down syndrome, Patau syndrome, Edwards syndrome, and Kleinfelter syndrome.
The second indicator is the presence or absence of monogenic diseases in the embryo. For example, cystic fibrosis, phenylketonuria, and others. There are more than 3000 such diseases in total. The chromosome set in monogenic diseases corresponds to the norm, but the production of certain proteins that are responsible for certain functions of the body is disrupted. Check for monogenic diseases must be done if both parents are carriers of monogenic diseases. In this case, the diagnosis is performed for abnormalities of a specific gene.
The third indicator is translocations. Translocations are chromosomal abnormalities that occur when a part of one chromosome joins with a part of another chromosome during cell division. For example, part five connects to part nine, and the second part of the ninth connects to another part of the fifth. Such translocations can have a significant impact on the reproductive function and viability of the embryo.
Indications for PGDparents carrying chromosomal and genetic diseases;miscarriage (more than two miscarriages);the age of the men older than 39 years;age of a woman over 34 years old;failed IVF attempts (more than two);
The procedure of PGD
All types of PGD are performed in the clinic according to the following scheme. First, the woman’s superovulation is stimulated, the follicles are punctured, and the resulting eggs are fertilized. All the resulting embryos are cultured to the blastocyst stage (this is the stage at which the embryo is implanted in the endometrium of a woman).
The blastocyst consists of an average of 100 cells. Part of the cells form the trophectoderm (future placenta), part – the internal cell mass (future fetus). Embryologists perform a biopsy of the trophectoderm, i.e. they take several (3-5) cells from it, without damaging the future fetus, and send them for genetic analysis. The embryo is frozen. The procedure is performed on high-tech equipment under a microscope using micromanipulators and a special laser installation. In this case, both the embryo and part of the cells sent for genetic analysis are marked strictly in accordance with the belonging of one to the other.
After that, some of the trophectoderm cells are analyzed by geneticists for the presence of chromosomal abnormalities, monogenic diseases or translocations. For each embryo, the geneticist gives a conclusion, on the basis of which the reproductologist together with the patient will be able to make a decision on the transfer of a specific embryo. On average, the PGD procedure takes 1 month.
The advantages of PGD
What are the alternatives to PGD? There are technologies that can also tell you about the genetic abnormalities of the fetus.Non-invasive prenatal testing, or NIPT. It can be performed from the 9th week of pregnancy. By this time, the mother’s blood already contains enough fetal DNA to assess the presence / absence of chromosomal abnormalities. After taking blood from a vein, the geneticist gives a conclusion on the basis of which the parents, together with the doctor, can decide to terminate the pregnancy at an early stage.Chorionic biopsy is an invasive diagnostic method that involves taking a small sample of tissue from the nascent placenta. The placenta in most cases has the same genetic material as the fetus. Therefore, based on the results of placental tissue analysis, it is possible to conclude about the genetic status of the fetus. Tissue is taken away using a needle, piercing the fetal bladder. In this connection, there may be a risk of violation of the course of pregnancy and even miscarriage.Amniocentesis-analysis of amniotic fluid. Like a chorion biopsy, amniocentesis is an invasive method. Only here the genetic status is determined by amniotic fluid, a sample of which is taken using a puncture in the abdomen under ULTRASOUND control.It can be concluded that PGD has undeniable advantages over alternative diagnostic methods: preimplantation genetic diagnosis makes it possible to find out the genetic status of the embryo before pregnancy and the subsequent need for termination in case of adverse results.The question of whether the PGD procedure is appropriate is decided on the basis of a joint consultation of a gynecologist-reproductologist and a geneticist, after careful acquaintance with the history of the couple, carrying out the necessary clinical, laboratory and instrumental studies.