A Fluorescence In-Situ Hybridization (FISH) test assesses the presence of chromosomal abnormalities on certain genetic locations that are crucial for new life.
The FISH test on sperm shows the proportion of chromosomal mistakes in men undergoing infertility investigation. The results of FISH are presented as the percentage of sperm cells that have chromosomal abnormalities in a semen sample.
The genetic material (DNA) is organized in a set number of chromosomes. There are 46 chromosomes in a human cell organized in 23 pairs, with 23 coming from a sperm and 23 from an egg. The loss of one or more chromosomes due to a genetic mistake accounts for a chromosomal abnormality called aneuploidy. Normally, all men have a 1.9-2% of sperm aneuploidy in their semen*. This may occur due to a mistake during production and maturation of sperm in the testes.
An increase in the percentage of sperms with aneuploidy has been associated with infertility, poor-outcome Assisted Reproductive Technique (ART) and repeated miscarriages.
With the FISH test on sperm, we look at specific chromosomal locations (chromosomes 13, 18, 21, X and Y) and estimate the risk of having embryos with chromosomal abnormalities. Some chromosomal mistakes are compatible with life (for instance, as it happens with babies born with Down or Turner syndromes), but most of them result in spontaneous miscarriages.
For cases involving a high percentage of sperm aneuploidy, we recommend Preimplantation Genetic Diagnosis (PGD) and / or Preimplanation Genetic Screening (PGS) of the early embryo. These genetic analyses will be able to identify abnormalities that have been passed onto the early embryo.
This test is recommended to men that have faced an infertility issue, and a classical semen analysis has not been able to pinpoint the problem.
It is also recommended to men that their semen analysis showed a high percentage of abnormal-shaped sperms (abnormal morphology orteratozoospermia), although aneuploidy can also occur to normal-shaped sperms.
Additionally, a FISH test on sperm is essential in cases that there has been a previous In-Vitro Fertilization (IVF) or implantation failure, unexplained infertility, or repeated miscarriages. Finding a high percentage of sperm chromosomal abnormalities might be the explanation in these instances.
High levels of sperm aneuploidy are often attributed to cigarette smoking, high caffeine intake, high alcohol or drug consumption, chemical, toxic or radiation exposure (including treatment for cancer), advanced paternal age and hormonal imbalances.
Sperm production in the testes is a continuous process, with a sperm maturation cycle taking about 11-12 weeks. Management of the above risk factor(s) may be able to reduce the levels of chromosomal abnormalities in sperm within a period of 3-6 months. In those cases, a repeat semen analysis and FISH test will show the improvement. However, the cause of high level sperm aneuploidy may sometimes be irreversible.
A FISH test on sperm is done by our andrology technologists in the laboratory following sperm collection for analysis.
After semen processing, isolated individual sperms are chemically fixed in their latest live state and two of our technologists check independently specific chromosomic locations in two sub-specimens of the investigated sample. To do that, they label chromosomes 13, 18, 21, X and Y with specific fluorescent probes and observe a representative amount of individual sperms microscopically. The results combine their individual observations and are presented as a percentage of aneuploidy for the sample as a whole.
A high-percentage of chromosomal abnormalities in sperm has been shown** to have a negative effect on pregnancy rates and it is normally associated with recurrent miscarriages, after a natural or an ART-mediated conception (for instance IVF, Intra-Cytoplasmic Sperm Injection, ICSI).
In some cases, where risk factors can be managed efficiently resulting in a lower percentage of sperm aneuploidy, the prospect of a successful ART increases (especially when other parameters, such as maternal age and egg quality are also optimal).
Here in AAFC, we use FISH test on sperm in conjunction with other diagnostic tests in order to understand persistent infertility, previous ART failure and repeated miscarriages. We can help you take an informed reproductive decision and offer you support, when necessary. Our specialist doctors will provide you with a comprehensive consultation for all other available / applicable options and explanations.
References
** Chatziparasidou A, Christoforidis N, Samolada G, Nijs M (2015). Sperm aneuploidy in infertile male patients: a systematic review of the literature. Andrologia. (8): 847-60. (Pubmed; PMID: 25352353)