Sperm morphology is one of the tests included in the seminogram, in which the percentage of spermatozoa with normal morphology is assessed. There are clinics that promote rutinary morphology checkups, while others do not consider the results to be relevant. In case of requiring an ICSI, the embryologist will choose with his own eyes the spermatozoid that, according to his/her judgement, matches the parameters of good aspect and motility.
A proper morphology is important, since the alterations can have a genetic cause, being the morphology a reflection of the mentioned cause. A spermatozoid whose genetic information —which contains only half the genetic information of the embryo— is not properly codified and organised will not produce a viable embryo.
Semen with morphology values that lay outside the lower normality levels presents teratozoospermia.
The different sections of this article have been assembled into the following table of contents.
Evaluation of sperm morphology
The first step to study the shape of the male gametes is to attach a small sample of the ejaculate into a slide, which implies the death of the sperm. Although this prevents the sample to be used after its evaluation, it may serve as representative of the rest of the sample which has not been used.
A biological staining is performed, such as the hematoxylin-eosin stain: the eosine is attached to the electropositive elements of the cell and is pink-coloured. The hematoxylin is attached to the electronegative molecules of the spermatozoa, obtaining a blue-toned coloration. The staining of these structures allow for a better microscope observation because the definition of the membranes has increased.
To assess the sperm morphology, three main structures should be observed:
- Head: it should be oval-shaped. It is a bad sign if the spermatozoid does not have acrosome (anterior half of the head), or if it is too round or slender. The head must be nearly fully occupied by the nucleus of the cell, without having too many vacuoles within. Vacuoles are organelles that appear often, but an excessive amount of them or an excessive size may entail a damaged DNA.
- Midpiece: it is located between the head and the flagellum (tail), and it is an area slightly broader than the base of the tail. It has a primordial function, as it hosts the mitochondria, responsible for generating energy, they are the moving force of the spermatozoid. The alterations that the midpiece may present are having a curvature, being thicker than the standard, having irregularities, or even being absent.
- Tail: the flagellum is composed of the same structural molecules responsible for the proper distribution of chromosomes in the mitosis and meiosis. An irregular flagellum will relflect problems in the share-out of chromosomes, and on top of that, its motility cannot compete against the hitting of a normal spermatozoid.
The duplication or absence of the aforementioned structures are evident sorts of alterations. Spermatozoa with two tails, microencephalic or macroencephalics ones will never naturally build a viable embryo.
In the early beginnings of the study of sperm morphology, there was a list of anomalies. A spermatzoid with any of the features listed would have good morphology. There were so many alterations that the scientifc community chose to standarise the strucuture of sperm with good morphology. Deviations from this pattern are considered alterations.
Spermatozoa with abnormal morphology may present anomalies in the head, midpiece and/or tail.
According to the WHO, values equal to or higher than 4% of spermatoza with proper morphology are considered normal. If the rate of abnormal spermatozoa is higher than 96%, it is called teratozoospermia.
However, there is a stricter criteria for the analysis of sperm morphology known as Kruger’s strict criteria. According to it, scores of greater than 14% indicate normal fertilization potential, that is to say, if there is sample in which abnormal sperm represent over 86%, the man concerned will be diagnosed of teratozoospermia.
Sperm morphology and fertility
Men with deterioration of sperm morphology, i.e. suffering from teratozoospermia, may face difficulties or even find it impossible to achieve a natural pregnancy.
Although teratozoospermia is not considered as a severe sperm-related problem, it is not unusual that men suffering from this condition have to resort to Assisted Reproductive Technology (ART) in order to become fathers, especially in most severe cases.
Depending on your condition and other factors affecting both male and female fertility, the most appropriate reproductive treatment will be indicated.
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