What Is Sperm Morphology? – Meaning & Normal Range

Sperm morphology is one of the aspects studied in the basic semen analysis or seminogram. Evaluating sperm morphology is used to see how many sperm are found with an abnormal shape and the type of alterations they present.

All men produce abnormally shaped sperm. In fact, in a semen sample considered normal, a large part of the sperm may have an altered morphology.

Despite this, if the seminogram does not find a minimum percentage of sperm with normal morphology, the man is said to have teratozoospermia.

How do I know if my sperm is normal?

In order to study the morphology of the spermatozoa, a small amount of semen is taken from the total ejaculate of the male. This semen sample is spread, fixed, and stained on a slide to facilitate its observation under the microscope, which implies the death of the spermatozoa.

Evaluating sperm morphology

This procedure, therefore, prevents these spermatozoa from being used after evaluation. However, the analysis of this small sample will serve as a proxy for the rest of the semen sample.

Normal sperm morphology

To evaluate the morphology of sperm, its three main structures are observed under a microscope: head, midpiece, and tail. Broadly speaking, the characteristics of sperm with normal morphology are the following:

• The head of the spermatozoon should be oval and smooth, 5 to 6 microns long and 2.5 to 3.5 microns wide. The acrosome should cover 40-70% of the head volume, and if there are vacuoles they should be scarce and occupy less than half of the head volume since if they are numerous or large it may mean that the DNA is damaged.
• The middle piece or neck, as its name indicates, is located between the head and the flagellum, and it is a slightly wider area than the base of the tail. Its function is primordial because it houses the mitochondria, considered the motor of the sperm's movement, as they are responsible for generating energy.
• The flagellum or tail is made up of the same structural molecules responsible for the correct distribution of chromosomes in mitosis and meiosis, so an irregular flagellum will reflect problems in the distribution of chromosomes, and above all, its movement will not be able to compete with the batting of a normal spermatozoon.

Spermatozoon with normal morphology

In this way, spermatozoa are evaluated individually, taking into account that a spermatozoon must be normal in all its parts to be considered morphologically normal. It should be noted that this evaluation can be subjective and subject to variation.

Generally, 200 spermatozoa are evaluated, noting whether their shape is normal or not. In addition, this evaluation should be done in duplicate. Subsequently, the percentage of spermatozoa with normal shape is calculated and presented in the seminogram results report.

Abnormal spermatozoa: causes and alterations

A high percentage of morphologically abnormal spermatozoa has been related to altered spermatogenesis, as well as to some pathologies of the epididymis.

Sperm with abnormal morphology can present defects in any of its parts (or in several). The following alterations can be found in each of the parts of the sperm:

• Head: headless spermatozoa (pinhead), small, amorphous, round, elongated, large, pear-shaped (pyriform) head, with large or small acrosome, vacuolated (with more of 2 vacuoles, vacuoles that occupy more than 20% of the head or with vacuoles in the postacrosomal region) or sperm with two heads.
• Midpiece: asymmetrical, thickened, thin, sharply curved, irregular, or with a bulge larger than one-third of the area of ​​the head.
• Tail: spermatozoa without a tail, short tail, multiple, coiled, broken, bent, with pronounced angles or of irregular thickness.

Types of sperm morphology alterations

However, headless or tailless sperm should not be counted, as they are not taken into account in the calculation of sperm concentration.

Abnormal morphology could affect a sperm's ability to fertilize. In addition, abnormal sperm may also have altered DNA.

Normal values

According to the criteria of the World Health Organization (WHO), a quantity equal to or greater than 4% of spermatozoa with normal morphology is considered normal. If the value of abnormal sperm is greater than 96%, that is, there are less than 4% normal sperm, the man has teratozoospermia.

Reference level for sperm morphology

There is another somewhat stricter morphology analysis criterion. This is the Kruger morphology criterion, according to which the limit of normality is 14%. This means that a sample with more than 86% of its sperm abnormal will be considered teratozoospermic.

Is there treatment or is there no solution?

Un hombre cuyos espermatozoides muestran una morfología alterada, es decir, padece de teratozoospermia, puede tener mayores dificultades de conseguir el embarazo de forma natural. Aunque la teratozoospermia no es uno de los problemas seminales más graves, es posible que sea necesario recurrir a la reproducción asistida para poder tener hijos propios, especialmente en los casos de teratozoospermia severe.

In milder cases, sperm morphology could be improved with a proper diet, reducing caffeine intake and avoiding tobacco and drugs.

Possible treatment of altered sperm morphology

There are also food supplements rich in antioxidants that prevent damage to sperm DNA caused by oxidative stress. These supplements contain vitamins and minerals necessary for proper male reproductive function. However, their benefits have not been scientifically demonstrated in a robust manner.

In milder cases, sperm morphology can be improved with an adequate diet, reducing caffeine consumption, and avoiding tobacco and drugs.

There are also specific food supplements that prevent damage to the DNA produced by free radicals and contain vitamins and minerals necessary for proper sperm production and maturation.

These supplements must be taken for at least 3 months, which is the time it takes for sperm to be produced from scratch and mature.

The Role of Assisted Reproduction

When a semen analysis reveals a very high percentage of abnormally shaped sperm, achieving pregnancy naturally can be difficult. In these situations, assisted reproductive technologies become the best option, as they allow these physical barriers to be overcome directly in the fertility laboratory. Specialists facilitate the process that the cells cannot carry out on their own due to structural defects.

In cases of severe teratozoospermia, the most commonly used and effective technique for addressing sperm morphology issues is Intracytoplasmic Sperm Injection, known as ICSI. During this procedure, the embryologist examines the semen sample under a microscope and visually selects the sperm with the best appearance and motility. Once selected, the embryologist injects it directly into the egg using a very fine microscopic needle, thereby ensuring the union of the two gametes.

By depositing the sperm directly inside the egg, it no longer matters whether the sperm had difficulty moving or whether its head was not shaped properly to penetrate the egg’s outer layer on its own. In this way, the work done in the laboratory helps significantly increase the chances of obtaining viable and healthy embryos, regardless of any initial abnormalities in the semen sample.

FAQs from users

How can sperm morphology be improved?

Sperm morphology is one of the most important determinations and one of the critical parameters in determining a man's ability to fertilize. Sperm morphology evaluates the morphometric characteristics of the sperm head, midpiece and tail.

Normal spermatozoa have an oval head and a long tail. In contrast, abnormal sperm have defects in the head or tail, such as a large or misshapen head or a double or crooked tail.

There are not many known factors that can improve sperm morphology and thus increase the percentage of normal forms.

It has been seen that the time sperm spend stored in the epididymis can be a determining factor in seminal quality; low ejaculatory frequency has been related to increased exposure to the effects of oxidative stress.

The time of sexual abstinence is one of the clinical criteria taken into account during seminal analysis; the interval recommended by the WHO is 2 to 7 days. Some studies have shown that increased ejaculatory frequency has positive effects on different conventional semen parameters, including sperm morphology.

In Assisted Reproduction, when performing IVF, we can improve fertilization results in cases of alterations in sperm morphology with intracytoplasmic sperm injection (ICSI). This technique makes it possible to select the spermatozoa at the time of fertilization also based on morphological criteria.

Can an abnormal sperm fertilize? Is pregnancy possible?

Yes, abnormal sperm is able to fertilize but most likely will not since those with normal shape move faster and will have it easier to reach the egg.

Depending on how the sperm are altered and how many abnormal sperm there are, the likelihood of pregnancy will be higher or lower.

For example, in spermatozoa without head (no genetic content) or with a small or absent acrosome (necessary to penetrate the egg) fertilization will not take place since they lack an essential part for the process.

Can abnormal sperm cause a miscarriage?

That might happen. The altered sperm may have genetic abnormalities that make it difficult or impossible for the embryo to form or develop, so it may not be viable and may stop growing, causing a miscarriage.

Depending on the gene or genes affected, embryonic development would stop at one point or another, depending on when they have to start expressing themselves; in other words, if the gene that is defective is very important in the first few weeks of pregnancy, an early abortion would occur because it does not contain adequate information for its development.

Can there be abnormal sperm from varicocele?

Varicocele is the cause of approximately 40% of male infertility cases. It produces a decrease in sperm production capacity, mainly due to an increase in testicular temperature and free radicals.

Therefore, it decreases both the concentration and the mobility of the spermatozoa and it seems that it is also related to the appearance of anomalies in the sperm morphology such as alterations in the head.

Is a semen sample considered normal if 95% of the sperm have abnormal morphology?

Yes, a semen sample containing as little as 5% of sperm with normal morphology would be considered normal (in terms of sperm morphology), even though it may seem otherwise.

Men produce many abnormally shaped sperm, which make up the majority of the sperm in the ejaculate. Therefore, according to the 2010 World Health Organization (WHO) criteria (the most widely used, despite a 2021 update), a semen sample can be considered normal for sperm morphology with as little as 4% normal forms.

However, percentages below 4% of normal sperm would indeed indicate a semen disorder known as teratozoospermia.

Recommended readings

If you want more information about the seminogram, you can visit the following link: What is a basic seminogram and how is it done step by step?

If, on the other hand, you want to know more about antioxidants to improve semen quality, we recommend you read this article: What are antioxidants and how do they affect semen quality?

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References

Authors and contributors

Marta Zermiani

M.D., Ph.D.

Gynecologist

Graduated in Medicine and Surgery from the Università degli Studi di Padova in Italy, specializing in Gynecology and Obstetrics at the Hospital Universitario de Bellvitge in Barcelona. Specialist in Assisted Reproduction with 4 years experience and currently a gynecologist at Vida Fertility Madrid. More information about Marta Zermiani

Licence number: 280847526

Marta Barranquero Gómez

B.Sc., M.Sc.

Embryologist

Graduated in Biochemistry and Biomedical Sciences by the University of Valencia (UV) and specialized in Assisted Reproduction by the University of Alcalá de Henares (UAH) in collaboration with Ginefiv and in Clinical Genetics by the University of Alcalá de Henares (UAH). More information about Marta Barranquero Gómez

License: 3316-CV

Sara Salgado

B.Sc., M.Sc.

Embryologist

Degree in Biochemistry and Molecular Biology from the University of the Basque Country (UPV/EHU). Master's Degree in Human Assisted Reproduction from the Complutense University of Madrid (UCM). Certificate of University Expert in Genetic Diagnosis Techniques from the University of Valencia (UV). More information about Sara Salgado

Silvia Azaña Gutiérrez

B.Sc., M.Sc.

Embryologist

Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez

License: 3435-CV

Cristina Algarra Goosman

B.Sc., M.Sc.

Psychologist

Graduated in Psychology by the University of Valencia (UV) and specialized in Clinical Psychology by the European University Center and specific training in Infertility: Legal, Medical and Psychosocial Aspects by University of Valencia (UV) and ADEIT.
More information about Cristina Algarra Goosman

Member number: CV16874