Although sperm production and subsequent fertility cannot be assessed purely on a single sample of semen, it can give insights that can help improve your chances of a successful pregnancy. Read on to learn more about what semen is and how it is produced, what a semen analysis looks for, and what this could mean for you.
What is a semen sample?
The male reproductive system is composed of the penis, testes, urethra, sperm ducts and the glands (see Figure 1). The testes are inside a pouch of skin called the scrotum. The role of the testes is to produce sperm and hormones. Once made in the testes, the sperm passes through the sperm ducts and mixes with fluids produced by the glands (seminal vesicles, prostate gland and bulbourethral glands), which provide nutrients to the sperm. This mixture of sperm and fluids is called semen (also known as ejaculate). The semen exits the body through a tube called the urethra inside the penis, which is also used to pass urine.
A semen sample is usually produced by semen manually collected via masturbation into a vial and analysed in a laboratory within one hour of collection. A semen sample must be obtained between two days of abstinence and seven days of abstinence.
Figure 1: Male reproductive organs
Analysis of a semen sample
Semen is collected and analysed at a laboratory to check for key characteristics (1):
- Physical properties of semen, such as semen volume, colour, odour, pH, viscosity, and liquefaction
- Spermatozoa (a mature sperm cell) count
- Non-sperm cell count
- Sperm motility
- Sperm vitality
- Sperm morphology
- Others
Physical properties of semen –
A normal semen sample is 1.5ml or more in volume, has a pH of 7.2 or more, and normally has a cream/grey-opalescent appearance, but may have a more yellowish appearance after a longer period of abstinence. (2)
The odour of ejaculate can vary for individuals, however should not have a strong odour, especially of urine. (1)
Semen is initially a semi-solid mass, but begins to liquefy (become thinner) within a few minutes in a process called liquefaction, which should occur within 15-30 minutes for a normal sample. (1)
- Once liquefaction is complete, it should have low viscosity (runnier) with no mucus strands in it. (1)
- Clumping in the sample may indicate that the spermatozoa is either sticking to each other or to mucus strands, non-sperm cells or debris. (1)
Spermatozoa count –
The normal total spermatozoa count is 39 million spermatozoa per ejaculate or more, and a sperm concentration of 15 million spermatozoa per ml or more. (2)
Non-sperm cell count –
Normal semen samples may contain cells other than spermatozoa, which could be problematic, e.g. the number of white blood cells or immature sperm cells is important. (1)
Sperm motility –
Sperm movement is divided into four groups, ranging from ‘rapidly progressive’ sperm, which have active sperm movements covering a large distance, to ‘immotile’ sperm, which show no active sperm tail movements.
- Progressive motility is movements that the sperm makes that move the sperm in a forward direction, rather than in a circular direction. Progressive sperm motility is related to pregnancy rates. (3)
Normal total motility, this means the percentage of progressive motility and non-progressive motility is 40% or more. (2)
Sperm vitality – describes how many sperm cells are alive
Sperm vitality is not so important when at least 40% of spermatozoa are motile. (1) If a semen sample has many spermatozoa which are not motile, then checking sperm vitality can show whether the spermatozoa are not moving because there is a problem preventing movement, or whether the spermatozoa are dead. Sperm vitality is considered normal if there are 58% or more live spermatozoa. (2)
Sperm morphology – describes the shape of the sperm
There is large variation in the shape of spermatozoa, but studies have identified the most likely shapes for fertilisation of an egg. Using this criteria, the head, neck, midpiece and tail of the spermatozoa are analysed to check for normal forms, and 4% or more is considered normal. (1,2)
Other tests
Other tests may be run to
- Check for anti-sperm antibodies
- Calculate the number of abnormalities seen per spermatozoa
- Check for spermatozoa DNA damage
- Analyse spermatozoa gene
- Count inflammation markers
- Check the function of the other male reproductive glands
- Check how well the spermatozoa can fertilise with the egg, which is especially important if the semen analysis shows otherwise ‘normal’ results.
If the results of the first semen analysis are abnormal, a further semen sample is taken and analysed after three months to allow time for new spermatozoa to be produced. One abnormal semen analysis is not a cause of concern, but those with two abnormal semen analysis results should be referred for further assessment by a healthcare provider. (2)
Although you may experience difficulties achieving a successful pregnancy if you have an abnormal semen analysis, it does not mean a successful pregnancy cannot be achieved. Speak to your healthcare provider if you are worried about any of the things mentioned in this article.
References:
- WHO. World Health Organization. WHO laboratory manual for the examination and processing of human semen. 6th ed. World Health Organization, Department of Reproductive Health and Research. Geneva, Switzerland. WHO Press. 2021.
- Quality statement 4: Semen analysis | Fertility problems | Quality standards | NICE [Internet]. Available from: https://www.nice.org.uk/guidance/qs73/chapter/quality-statement-4-semen-analysis
- Zinaman MJ, Brown CC, Selevan SG, Clegg ED. Semen quality and human fertility: A prospective study with healthy couples. J Androl. 2000;21(1):145–53.
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