Preimplantation diagnosis of the embryo by FISH

Fluorescence in situ hybridization (FISH) is one of the methods of preimplantation genetic diagnosis (PGD), which is carried out at theIVMEDclinic as part of IVF. Fluorescence in situ hybridization allows us to select healthy embryos without chromosomal abnormalities for transfer to the uterus. This increases the likelihood of a successful IVF program, reduces the risk of spontaneous abortion, and reduces the likelihood of having a sick child.

The FISH method increases the HDP:

• the likelihood of selecting and transferring only healthy embryos (without chromosomal abnormalities) to the uterus;
• chances of successful embryo implantation;
• prospects for a safe birth of a child.

Reduces:

• the risk of having a child with chromosomal diseases;
• the likelihood of miscarriage;
• risk of stillbirth or early infant mortality.

FISH diagnostics combines the advantages of cytological, cytogenetic and the latest molecular methods. The object of study is the unique nucleotide sequences of a particular chromosome or its separate part.

Translocations are the most frequent structural chromosomal rearrangements that do not manifest themselves phenotypically in carriers. Translocations can lead to infertility, miscarriage, stillbirth or early infant mortality, and the birth of children with chromosomal abnormalities.

As a method of preimplantation genetic diagnosis, FISH allows to determine aneuploidies of chromosomes 13, 15-18, 21, 22, as well as X- and Y-chromosomes and to detect chromosomal rearrangements.

In theIVMEDclinic, PGD by FISH is performed on the 5th day of embryo development, which allows obtaining more accurate and detailed information about its chromosome set.

Advantages of FISH diagnostics on the 5th day of embryo development:

• all embryos that have reached the blastocyst stage (i.e., have a high potential for further successful development) are examined;
• it is possible to extract more cells for research (than on the 3rd day of development) without harming the embryo;
• low risk of embryo mosaicism (due to the self-correction mechanism);
• high embryo implantation rate.

Who undergoes FISH diagnostics

FISH is used in the following cases:

• if the expectant mother is 35 years old or older;
• if the future father is 42 years old or older;
• a man was diagnosed with spermatogenesis disorders;
• the woman has a history of 2 or more failed IVF attempts or 2 or more cases of miscarriage.

Diagnosis is recommended if the parents have a recessive X-linked disease, in the presence of deletions in the Y chromosome.

Features of the FISH method

• 97% – reliability of the results of preimplantation genetic diagnostics;
• 70% higher probability of IVF success on the first attempt;
• less than 0.5% – risk of embryo damage during trophectoderm biopsy;
• 2 times lower risk of multiple pregnancy and miscarriage;
• 10% higher probability of successful implantation of the embryo in the uterus;
• 20% higher chances of a safe birth.

The procedure for performing preimplantation diagnostics by FISH

1. Fluorescence in situ hybridization allows hybridization of both metaphase and interphase chromosomes using different DNA probes. Probes are cloned sequences or isolated DNA regions that are complementary to the DNA regions of the sample under study. DNA probes are labeled with fluorescent substances.
2. The sample for the study is obtained on the 5th day of embryo development (blastocyst stage). The procedure is called a trophectoderm biopsy and consists in removing several cells from the outer layer of the embryo (the inner cell mass, which is the basis for the formation of fetal organs, is not affected).

The laboratory stage of PGD by FISH includes the following manipulations:

1. A probe is prepared for the chromosome (or a part of it). This is a single-stranded DNA region to which fluorescent tags are attached.
2. Using a special drug, DNA is denatured, i.e., the hydrogen bonds between the double strands of DNA are broken.
3. The sample is processed using DNA probes. The DNA strands of the sample and the probe are complementary, so the probe connects to the corresponding part of the chromosome, and the DNA double helix is restored (the renaturation process occurs).
4. The sample is treated with chemical compounds that selectively bind to the fluorescent tags.
5. Fluorescent dyes are added to the resulting complexes.
6. Thanks to the fluorescent microscope, you can see stained and unstained chromosomes.
7. A genetic laboratory specialist analyzes the data and draws up a conclusion on the presence/absence of chromosomal translocations and aneuploidies.
8. As a person ages, chromosomal abnormalities occur in reproductive cells (eggs and sperm), which reduce the chances of pregnancy and lead to habitual miscarriage or frozen pregnancy. PGD by FISH, which can be performed as part of IVF, allows you to select the most promising embryos for transfer to the uterus to increase the chances of successful implantation of the embryo in the uterus, gestation and birth of a healthy child.
9. To become parents of a long-awaited healthy baby, use the preimplantation genetic diagnosis FISH at theIVMEDclinic.