The aim of the semen analysis is to estimate or measure the three principle ‘sperm quality measures’ where possible. These include:
This is also known as the sperm count, and it’s measured in millions per ml. Increasing sperm concentration and the total sperm number (the sperm concentration X semen volume in mls) are both related to the chance of pregnancy, whether it occurs naturally or by assisted conception.
Sperm motility is the swimming ability of the sperm population, and the most important function that we can assess.
In many centres this just means the number of sperm swimming in a forward direction – however the scientific evidence suggests that this can be misleading, as they could be sluggish and incapable of making the journey. Therefore we also want to know how fast the sperm swim. To do this properly, it must be measured at 37⁰C using a computer.
Sperm count is often measured manually using a specialised cell counting chamber (haemocytometer) under the microscope. Motility can also be assessed manually, but is almost impossible to perform with any real accuracy since the sperm are constantly swimming in and out of view.
We therefore choose to use a computer (below) to take a short 1-second video of sperm, and use this to assess both sperm concentration (sperm number) and motility at the same time. Computer algorithms help the software to distinguish sperm that overlap as they swim, and minimise error in assessing the percentage that swim and how fast they go. This is called CASA, or computer assisted semen analysis and a major advantage that CASA has over other methods, is that for any given test or sample, the lab will get the same results, no matter which member of staff performs it.
Video generated by CASA. Sperm are tracked for 1 second to give individual sperm swimming speeds. By limiting the field to only a second we minimise ‘over-estimation’ of the motile sperm fraction as they leave and enter the area whilst being examined down the microscope. Only those sperm that can be followed for the full 1 second are assessed.
This is probably the most controversial sperm parameter assessed, as it is very subjective and open to interpretation.
No-one really can tell whether an individual sperm looks fertile or not, and the most recent scientific evidence from large studies in IVF suggest that the % of what we perceive as ‘normal sperm’ does not predict whether your treatment will be successful or not.
However this does not mean that sperm morphology is unimportant, as we know that sperm of certain shape, size and structure are incapable of reaching and fertilising the egg. (For example, the 3-headed sperm pictured here).
Other important measures of sperm/semen quality
Ejaculate volume: Measured in mls, a normal volume should be around 1.5mls (under half a teaspoon).
Having a normal volume shows us that the glands, such as the prostate and seminal vesicles, are working properly. A very low volume or no fluid at all (0.5ml) can indicate that the semen is going into the bladder instead (known as retrograde ejaculation). Click here for more on what can be done about retrograde ejaculation.
pH: Semen pH should be slightly alkaline (usually between 7.2-8.3). A low pH with an absence of sperm can indicate a blockage or obstruction – known as obstructive azoospermia.
Agglutination and Aggregation: The importance of this is often under-estimated. Live sperm can stick to each other which stops them from swimming. Not only is this an indicator for infertility, but this problem can progress with time.
It also means that estimating sperm number and motility is very difficult and often inaccurate, because all of our methods rely on us having the sperm evenly spread throughout the sample.
Other sperm tests
Antibodies to a man’s sperm have been suggested to be a cause of infertility for many years. They are strongly linked with reduced sperm motility (swimming ability) and agglutination (see above), but there is no evidence other than this that antibodies are produced which may block fertilisation.
Since both poor motility and agglutination are evident from the semen analysis without further testing, the test is considered largely redundant
DNA fragmentation and Reactive oxygen species
High levels of DNA fragmentation (DNA damage) has been associated with poorer sperm quality and, according to some studies, reduced chance of conception. However the strongest published evidence links sperm DNA damage to a higher chance of miscarriage. There are 4 or 5 published tests of DNA fragmentation, but no agreement amongst professionals as to which gives the most reliable results. Although we should not ignore evidence going back over the past 20 years, any test of DNA fragmentation is unlikely to affect the management of a couple’s infertility or choice of treatment. This is why it’s not routinely offered by the NHS, nor is it part of standard guidance from the WHO.
The same is true for reactive oxygen species (ROS). Although ROS are implicated in a number of disease processes, there is no way to say that the ROS levels in semen are so high that you cannot achieve a pregnancy. In addition, samples with both high levels of DNA damage and ROS usually have other more obvious problems, such as low sperm count, motility or poor morphology.
If there was a sufficiently reliable DNA or ROS test that would provide information that would change how your treatment is planned, both NUH Life and the NHS in general would be providing this routinely. In other countries the tests may be more widely offered, but usually the patient will be asked to pay for this.
Collecting a semen sample for testing
Everyone is different – collecting a sample for testing sperm quality can be a tricky and embarrassing process for some, and yet relatively straight forward for others. Click here for more details on specimen collection and how it is done, or feel free to download our leaflet on semen analysis by clicking on the link below.