How does semen density affect fertility?

By (embryologist), (gynecologist) and (embryologist).
Last Update: 05/10/2021

Many men wonder if their semen is too thick or, on the contrary, if it is too liquid. Sperm density varies not only from man to man, but also in the different ejaculations of the same man. This may depend on several factors such as, for example, the time of abstinence from ejaculation. Thus, with less time of abstinence the semen will probably be more watery.

When sperm is expelled in ejaculation it should have a thick consistency. However, a very dense ejaculate can affect other seminal quality parameters such as sperm motility. Therefore, abnormally thick semen could lead to male fertility problems.

Thick or liquid sperm?

The semen has a certain density after ejaculation, as this ensures that a greater number of sperm reach the bottom of the vagina. It is important to remember that the sperm's ultimate goal is to fertilize the egg. To do this, the sperm must travel a long way until they reach the fallopian tubes, where they meet the oocyte.

To make it easier for as many sperm as possible to reach the bottom of the vagina, the semen forms a kind of clot immediately after it is expelled. This is mainly due to the semenogelin proteins. These proteins are produced by the seminal vesicle and are responsible for the sperm acquiring a dense, jelly-like consistency.

Once in the female reproductive tract, the sperm must move upward. The prostate specific antigen (PSA) fragments the semenogelin, which allows the semen to liquefy within 15-20 minutes after being expelled. Thus, once the semen has liquefied, the sperm can move and advance along the costly path of the female reproductive tract.

If the semen were completely liquid after expulsion, it would leak out of the vagina more easily and pregnancy would be more difficult to achieve.

Ejaculate viscosity

The viscosity of the semen sample must be taken into account in the spermiogram when analyzing semen quality. As mentioned above, a very thick semen sample can lead to sperm motility problems, making fertilization difficult.

Fertility treatments, like any other medical treatment, require that you trust the fertility specialists that will be by your side during your journey. Logically, each clinic has a different work methodology. Our Fertility Report will offer you a selection of recommended clinics, that is, fertility centers that have passed our rigorous selection process. Moreover, our system is capable of comparing the costs and conditions of each one so that you can make a well-informed decision.

Some of the reasons that can cause a variation in semen viscosity are:

Bearing in mind these causes, it is advisable to consult a doctor if changes in the consistency or viscosity of the semen are observed in order to find out what may be causing it.

Semen composition

Semen is made up of a set of substances that are responsible, among other things, for it acquiring the consistency and density required to fertilize the oocyte. Approximately, only 5% of the semen content is spermatozoa, while the seminal plasma confers the remaining 95% of its consistency.

Sperm must travel from the testicle to the penis. On this path, the sperm mix with the seminal plasma produced mainly by the seminal vesicle and the prostate. Thus, the sperm is formed with the necessary molecules to give it its viscosity and subsequent liquefaction.

The seminal vesicle provides approximately 65% of the volume of semen. This contribution contains cytokines, prostaglandins, semenogelins and fructose.

The prostate secretes 25% of the seminal volume. Its secretion is rich in lipids, citrate and protein breaking enzymes (proteolytic).

The urethral and bulbourethral glands also contribute to sperm composition. These glands provide a lubricating secretion that accounts for about 1% of the total semen.

FAQs from users

Does the colour of the ejaculate indicate that it is too thick?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

The colour of the ejaculate can be helpful when analysing semen quality. A very transparent semen colour may indicate low sperm concentration and/or a more watery or liquid consistency.

Conversely, a deep white colour may indicate a higher sperm concentration.

Is it possible to achieve pregnancy with thick, clumpy sperm?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

As mentioned above, very viscous and lumpy semen can complicate the search for pregnancy because the high density can hinder the proper movement of the sperm and therefore prevent them from reaching the egg.

Although a certain density and consistency is needed during ejaculation, once in the vagina, the semen must liquefy so that the sperm can "swim" to the egg and fertilise it.

What are the causes of very thick semen?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

The most common causes of increased semen density are high sperm concentration, malfunctioning of the prostate and/or seminal vesicles, and the presence of seminal infections.

Suggested for you

If you would like more information about this sperm alteration, you can visit the link: Semen Quality : What Is Measured And What Can Be Done To Improve It?

If, on the other hand, you are interested in knowing more about the spermiogram or semen analysis, we recommend you to read this article: What Is a Semen Analysis Report? - Purpose, Preparation & Cost.

We make a great effort to provide you with the highest quality information.

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Anamthathmakula P, Winuthayanon W. Mechanism of semen liquefaction and its potential for a novel non-hormonal contraception†. Biol Reprod. 2020 Aug 4;103(2):411-426.

Drabovich AP, Saraon P, Jarvi K, Diamandis EP. Seminal plasma as a diagnostic fluid for male reproductive system disorders. Nat Rev Urol. 2014 May;11(5):278-88.

de Lamirande E. Semenogelin, the main protein of the human semen coagulum, regulates sperm function. Semin Thromb Hemost. 2007 Feb;33(1):60-8.

de Lamirande E, Yoshida K, Yoshiike TM, Iwamoto T, Gagnon C. Semenogelin, the main protein of semen coagulum, inhibits human sperm capacitation by interfering with the superoxide anion generated during this process. J Androl. 2001 Jul-Aug;22(4):672-9.

Lilja H, Oldbring J, Rannevik G, Laurell CB. Seminal vesicle-secreted proteins and their reactions during gelation and liquefaction of human semen. J Clin Invest. 1987 Aug;80(2):281-5.

Owen DH, Katz DF. A review of the physical and chemical properties of human semen and the formulation of a semen simulant. J Androl. 2005 Jul-Aug;26(4):459-69.

Samanta L, Parida R, Dias TR, Agarwal A. The enigmatic seminal plasma: a proteomics insight from ejaculation to fertilization. Reprod Biol Endocrinol. 2018 Apr 28;16(1):41.

World Health Organization (WHO) (2010). WHO laboratory manual for the Examination and processing of human semen. 5th ed. Geneva: WHO Press;2010.

FAQs from users: 'Does the colour of the ejaculate indicate that it is too thick?', 'Is it possible to achieve pregnancy with thick, clumpy sperm?' and 'What are the causes of very thick semen?'.

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Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo
 Rut Gómez de Segura
Rut Gómez de Segura
Graduation in Medicine and Surgery from the University of Alcalá de Henares. Specialization in Obstetrics and Gynecology at the Hospital Costa del Sol in Marbella. Dr Rut Gómez de Segura currently works as medical director in the fertility center ProcreaTec in Madrid. More information about Rut Gómez de Segura
Licence number: 28/2908776
 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
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

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