What information does the sperm analysis provide us according to the FISH method?

The FISH method for sperm diagnosis allows the detection of chromosomal abnormalities (aneuploidies), which are a major cause of male infertility, pregnancy failures, and IVF failures, and helps to choose the best treatment strategy.

Fundamental principles of the method

FISH, or fluorescence in situ hybridization, is a modern molecular cytogenetic method used to diagnose genetic factors of male infertility. Its importance is invaluable, as a standard semen analysis only provides a superficial idea of male fertility. While a semen analysis records the number of spermatozoa, their motility, morphological characteristics, detects cell agglutination (agglutination), and other indicators, it does not reflect the state of sperm DNA and chromosomal composition. These indicators are of crucial importance for conception and the birth of a healthy child.

That is why a comprehensive examination of the male factor of infertility must include additional methods, among which FISH analysis plays a special role. Its main goal is to evaluate the karyotype of spermatozoa and detect the presence of aneuploidy, i.e., chromosomal number anomalies. To do this, special DNA probes labeled with fluorescent dyes are used, which allow visualization of the chromosomes under a microscope.

The chromosomal heritage of spermatozoa and the importance of aneuploidies

Normally, spermatozoa are haploid cells containing 23 chromosomes, exactly half of the human genetic material. However, the process of sperm formation (gametogenesis) is imperfect. In each man, a certain percentage of spermatozoa have chromosomal anomalies. If this percentage exceeds the physiological norm, it can lead to serious reproductive problems.

The FISH testing panel generally includes the study of sex chromosomes (X and Y), as well as autosomes 13, 18, and 21, as these are most often associated with known syndromes: Klinefelter (XXY), Turner (X), Patau (trisomy 13), Edwards (trisomy 18), and Down (trisomy 21). If necessary, the scope of the analysis can be expanded, for example by adding chromosomes 16 and 22 in cases of recurrent miscarriages or examining chromosomes where chromosomal abnormalities have been detected in the man.

How does the FISH analysis proceed?

The examination is performed on a semen sample provided by the patient after a minimum abstinence period (usually 3 days). The technique involves several successive steps:

1. Fixation of spermatozoa on a microscope slide.
2. DNA denaturation: a process during which hydrogen bonds between DNA strands are destroyed, making the molecule single-stranded.
3. Hybridization of fluorescent DNA probes with target sites on chromosomes.
4. Removal of excess probes and staining of the sample.
5. Visualization of the signals under a fluorescence microscope and interpretation.

Normal spermatozoa emit a single fluorescent signal for each examined chromosome. Any deviation from this standard indicates aneuploidy.

Indications for the test

FISH analysis is used in cases where a more in-depth assessment of the man's genetic status is necessary :

• The man is over 40 years old.
• Presence of pronounced abnormalities in semen parameters.
• Miscarriages, fetal development arrest, or recurrent pregnancy loss.
• Chromosomal anomalies diagnosed in the fetus during previous pregnancies.
• Repeated unsuccessful attempts at IVF in vitro fertilization with no embryo implantation after transfer.
• Carrying balanced chromosomal rearrangements.

Men with a high rate of aneuploidy according to the results of the analysis are at significant risk of forming embryos with genetic anomalies, which reduces implantation chances, increases the risk of pregnancy loss, and the possibility of giving birth to a child with a karyotype abnormality.

Link with IVF and PGT-A

If high levels of chromosomal anomalies are detected in a man's sperm, the next step is to perform preimplantation genetic testing (PGT-A) on embryos. Combined with IVF programs, this allows selecting an euploid embryo for transfer, greatly increasing the chances of pregnancy and the birth of a healthy child. Thus, the FISH analysis closely integrates into modern assisted reproductive medicine methods and constitutes an important element of personalized infertility treatment.

In our blog, we addressed the question « What you need to know about preimplantation genetic testing (PGT-A)? »

Advantages of the method

• Improved diagnosis and treatment of infertility. The results help doctors choose optimal methods, including ICSI and IVF with PGT-A.
• Reduction of genetic risks. Provides precise information on the likelihood of transmitting chromosomal anomalies to offspring.
• Personalized protocols. Ability to create an individual treatment plan.
• Enhanced effectiveness of ART programs. Improves selection of high viability embryos.
• Minimal invasiveness. The method is performed on a semen sample without complex procedures.

Limitations of the method

Despite its high value, FISH also has certain limitations:

• The number of spermatozoa examined is limited, which risks missing rare anomalies.
• Even if results are normal, other factors of infertility cannot be excluded.
• The method requires specialized equipment and experienced personnel.

Interesting facts

• The name FISH stands for « Fluorescence In Situ Hybridization ». It is metaphorically called « fish » because probes « swim » and bind to chromosomes, creating bright luminous signals.
• This technology is used not only in reproductive medicine but also in oncology for cancer cell diagnosis, as well as in other areas of molecular genetics.
• FISH is an important complement to traditional cytogenetic methods, as it allows for faster and more precise detection of anomalies that might be missed with standard approaches.

The FISH analysis of sperm remains one of the key tools in reproductive medicine and genetics. Thanks to its precision, informative richness, and efficiency, it helps doctors and patients make informed decisions, improve IVF outcomes, and achieve the birth of healthy children.