Semen analysis
A semen analysis, also called seminogram or spermiogram, evaluates certain characteristics of a male's semen and the sperm contained therein. It is done to help evaluate male fertility, whether for those seeking pregnancy or verifying the success of vasectomy. Depending on the measurement method, just a few characteristics may be evaluated or many characteristics may be evaluated. Collection techniques and precise measurement method may influence results. The assay is also referred to as ejaculate analysis, human sperm assay, sperm function test, and sperm assay.
Semen analysis is a complex test that should be performed in andrology laboratories by experienced technicians with quality control and validation of test systems. A routine semen analysis should include: physical characteristics of semen, volume, concentration, morphology and sperm motility and progression. To provide a correct result it is necessary to perform at least two, preferably three, separate seminal analyses with an interval between them of seven days to three months.
The techniques and criteria used to analyze semen samples are based on the WHO manual for the examination of human semen and sperm-cervical mucus interaction published in 2021.
Reasons for testing
The most common reasons for laboratory semen analysis in humans are as part of a couple's infertility investigation and after a vasectomy to verify that the procedure was successful. It is also commonly used for testing human donors for sperm donation, and for animals semen analysis is commonly used in stud farming and farm animal breeding.Occasionally a man will have a semen analysis done as part of routine pre-pregnancy testing. At the laboratory level this is rare, as most healthcare providers will not test the semen and sperm unless specifically requested or there is a strong suspicion of a pathology in one of these areas discovered during the medical history or during the physical examination. Such testing is very expensive and time-consuming, and in the U.S. is unlikely to be covered by insurance. In other countries, such as Germany, the testing is covered by all insurances.
Relation to fertility
The characteristics measured by semen analysis are only some of the factors in semen quality. One source states that 30% of men with a normal semen analysis actually have abnormal sperm function. Conversely, men with poor semen analysis results may go on to father children. In NICE guidelines, mild male factor infertility is defined as when two or more semen analyses have one or more variables below the 5th percentile, and confers a chance of pregnancy occurringnaturally through vaginal intercourse within two years similar to people with mild endometriosis.
Collection methods
Methods of semen collection include masturbation, condom collection, and epididymal extraction. The sample should never be obtained through coitus interruptus as some portion of the ejaculate could be lost, bacterial contamination could occur, or the acidic vaginal pH could be detrimental for sperm motility.The optimal sexual abstinence for semen sampling is two to seven days. The most common way to obtain a semen sample is through masturbation or withdrawal method and the best place to obtain it is in the clinic where the analysis will take place in order to avoid temperature changes during the transport that can be lethal for some spermatozoa.
Once the sample is obtained, it must be put directly into a sterile plastic receptacle and be handed to the clinic for it to be studied within the hour.
There are some situations that necessitate alternative collection methods, such as retrograde ejaculation, neurological injury or psychological inhibition. Depending on the situation, specialized condoms, electrostimulation or vibrostimulation might be used.
Parameters
The parameters included in the semen analysis can be divided in macroscopic and microscopic. The main three parameters of the spermiogram are the concentration of the spermatozoa in the semen, the motility and the morphology of them. This analysis is important to analyse fertility, but even in a perfectly fertile man is very difficult to find normal spermatozoa. For the average fertile man, only 4% of their spermatozoa are normal in every parameter, while 96% are abnormal in at least one of them.Sperm count
Sperm count, or sperm concentration to avoid confusion with total sperm count, measures the concentration of sperm in ejaculate, distinguished from total sperm count, which is the sperm count multiplied with volume. Over 16 million sperm per milliliter is considered normal, according to the WHO in 2021. Older definitions state 20 million. A lower sperm count is considered oligozoospermia. A vasectomy is considered successful if the sample is azoospermic. Cryptozoospermia is when a sample contains less than 100,000 spermatozoa per milliliter. Some define success as when rare/occasional non-motile sperm are observed. Others advocate obtaining a second semen analysis to verify the counts are not increasing and others still may perform a repeat vasectomy for this situation.Chips for home use are emerging that can give an accurate estimation of sperm count after three samples taken on different days. Such a chip may measure the concentration of sperm in a semen sample against a control liquid filled with polystyrene beads.
Sperm motility
The World Health Organization has a value of 40% and this must be measured within 60 minutes of collection. WHO also has a parameter of vitality, with a lower reference limit of 60% live spermatozoa. A man can have a total number of sperm far over the limit of >16 million sperm cells per milliliter, but still have bad quality because too few of them are motile. However, if the sperm count is very high, then a low motility might not matter, because the fraction might still be more than 8 million per millilitre. The other way around, a man can have a sperm count far less than 20 million sperm cells per millilitre and still have good motility, if more than 60% of those observed sperm cells show good forward movement - which is beneficial because nature favours quality over quantity.A more specified measure is motility grade, where the total motility and immotile.
Progressively motile- Sperm moving in forward direction is Progressively Motile
Non progressively Motile-Those sperms are moving circular motion are Non Progressively Motile
Immotile- Those sperms are fail to move or dead sperms.
The total motility reference of 40% can be divided in a 32% of progressive motility and 8% of motility in situ.
Semen samples which have more than 30% progressive motility are considered as normozoospermia. Samples below that value are classified as asthenozoospermia regarding the WHO criteria.
Sperm morphology
Regarding sperm morphology, the WHO criteria as described in 2021 state that a sample is normal if 4% or more of the observed sperm have normal morphology. If the sample has less than 4% of morphologically normal spermatozoa, it's classified as teratozoospermia.Normal sperm morphology is hard to classify because of lack of objectivity and variations in interpretation, for instance. In order to classify spermatozoa as normal or abnormal, the different parts should be considered. Sperm has a head, a midpiece and a tail.
Firstly, the head should be oval-shaped, smooth and with a regular outline. What is more, the acrosomal region should comprise the 40–70% area of the head, be defined and not contain large vacuoles. The amount of vacuoles should not excess the 20% of the head's area. It should be 4–5 μm long and a width of 2,5–3,5 μm.
Secondly, the midpiece and the neck should be regular, with a maximal width of 1 μm and a length of 7–8 μm. The axis of the midpiece should be aligned with the major axis of the head.
Finally, the tail should be thinner than the midpiece and have a length of 45 μm approximately and a constant diameter along its length. It is important that it is not rolled up.
Since abnormalities are frequently mixed, the teratozoospermia index is really helpful. This index is the mean number of abnormalities per abnormal sperm. To calculate it, 200 spermatozoa are counted. From this number, the abnormalities in head, midpiece and tail are counted, as well as the total abnormal spermatozoa. Once that task has been done, the TZI is calculated like this:
TZI= /x
- x = number of abnormal spermatozoa.
- h = number of spermatozoa with head abnormalities.
- m = number of spermatozoa with midpiece abnormalities.
- t = number of spermatozoa with tail abnormalities.
The TZI takes values from 1 to 3.
Morphology is a predictor of success in fertilizing oocytes during in vitro fertilization.
Up to 10% of all spermatozoa have observable defects and as such are disadvantaged in terms of fertilising an oocyte.
Also, sperm cells with tail-tip swelling patterns generally have lower frequency of aneuploidy.