The analysis of freshly ejaculated semen is the most important diagnostic tool in the initial investigation of male fertility. Semen is a mixture of secretions from several components of the genital tract. The testis contributes only 5% of the semen volume but, naturally, all of the sperm.
During ejaculation, this fluid moves up through the epididymis and vas. Most of the seminal fluid is produced by glands at the base of the bladder, particularly the seminal vesicles and prostate.
The first part of the ejaculate contains the highest sperm number with the best motility. The proper assessment of semen quality in a semen analysis is essential in the diagnosis of several treatable disorders of male fertility. In many male factor patients, however, no specific treatment is available to improve semen quality in which case the semen analysis provides important information about the prospects for natural pregnancy and the use of assisted reproduction.
Is Semen Analysis An Accurate Test For Fertility?
The semen analysis provides an indication of male fertility but is not an absolute test for fertility because it does not assess important aspects of sperm function, for example the ability of the sperm to locate and penetrate an egg. Furthermore the finding of poor semen quality points to a reduced chance of pregnancy, however natural conception may still occur in some cases. However the more severe the semen defects, the lower the chances.
Routine Semen Analysis
For the semen analysis result to be most valuable, proper collection of the specimen is essential. The semen analysis is performed on a fresh specimen within 2 hours of collection. Before testing, a period of 2 to 5 days of abstinence from ejaculation is recommended. Feelings of anxiety about producing a specimen are common and should be discussed with the doctor or nurse.
Semen Collection Methods
The specimen is best collected by masturbation into a sterile container. This is most conveniently performed in the facility provided at the laboratory however collection at home is acceptable provided the sample is rapidly transported (within 1 hour) and kept at body temperature.
Semen collected by interrupted intercourse is not favoured as it risks the loss of sample, particularly the first fraction of the ejaculate.
Semen should never be collected into an ordinary condom, which contains substances that kill sperm.
If religious or personal practises prohibit masturbation, a special condom (SCD) can be used that does not affect the sperm quality.
The Semen Analysis
Laboratories vary widely in their ability to provide high quality analyses. Semen analyses are best performed in a specialised laboratory with extensive experience using the approved methods of the World Health Organisation.
Analysis of the ejaculate includes the characteristics of the seminal fluid (volume, pH) and of the sperm themselves including the number of sperm (called sperm ‘count’ or concentration), their movement (motility) and shape (morphology).
Normal Values Of Semen Variables
The normal ranges for various parameters of semen quality are shown below:
- Standard Tests Volume >2.0 ml.
- Sperm Concentration >20 million sperm/ml.
- Sperm Motility >50% with forward movement
- Sperm Morphology >15% normal forms
- White Blood Cells <1 million cells/ml.
- Sperm Antibodies (Immunobead Tests) <50% sperm with adherent particles
It is important to recognise that an individual’s semen quality can vary considerably between samples, even in men with normal semen parameters. As a result at least two, and occasionally three, semen analyses are needed, each several weeks apart, in order to get a good idea of an individual’s average semen quality. It is well recognised that sperm count can be adversely affected by illness, especially fevers, which may temporarily suppress sperm count in normal men for the several months. In this case the semen analysis should be delayed for several months.
The finding of no sperm in the ejaculate (called ‘azoospermia’) suggests either an absence of sperm production or obstruction to sperm outflow. It is most important that an azoospermic semen sample is spun down to carefully examine whether the ejaculate contains even a few sperm. If a few sperm can be found (called ‘virtual azoospermia’) the technique of single sperm microinjection (also called IntraCytoplasmic Sperm Injection, ICSI) may be successful. In these severely infertile men sperm may be appear only intermittently underlining the need for several semen analyses.
Sperm Motility (Movement)
Along with a low sperm count, sperm motility is often impaired in men with ‘idiopathic’ (meaning the cause unknown) poor sperm production. However there are other important conditions which predominantly effect sperm motility, such as sperm autoimmunity, a condition that accounts for about 6% of male infertility. Sperm that show no movement (immotile sperm) may be due to structural problems in the sperm tail or be due to death of sperm (necrospermia). Such couples have an exceedingly low chance of natural fertility but ICSI may provide an alternative.
The immune system produces antibodies as part of the normal defence against foreign substances and organisms. Sperm are normally protected from exposure to immune system. However some men produce sperm antibodies, following surgery (eg vasectomy) or trauma to the testicles. In other men there is no apparent cause for their development. The antibodies attach to the surface of the sperm and reduce their life span, impair sperm motility and ability to penetrate the partner’s cervical mucus. Finally antibodies located on the sperm head may prevent the sperm fertilising the egg.
Assessment for sperm antibodies is an essential initial test in suspected impaired fertility. The immunobead technique is a simple test that can be used to detect antisperm antibodies in blood or semen.
Sperm Morphology (Shape)
Sperm shape is an important predictive indicator of sperm fertilising ability. Compared with other species, the human has a relatively small percentage of sperm showing a ‘normal’ morphology (actually defined as being ideally shaped), with as few as 15% normal forms being regarded as the lower limit of normal. Fertility declines as this percentage falls, particularly in men with ejaculates with less than 5% normal-shaped sperm.
This assessment requires great skill and experience. Sperm are specially stained and viewed under a microscope, with assessment of the head, middle and tail regions. Many structurally abnormal sperm have many defects, which may affect all regions of the sperm.
Other Semen Assessments
The percentage of sperm that are alive (sperm vitality) is noted because this declines in association with genital tract infections and disorders of sperm transport through the genital tract.
The white blood cell count is also a marker of possible genital tract infections. Even in the absence of a relevant history or symptoms, the finding of a high white cell count may prompt investigation of infection and may warrant a course of appropriate antibiotic therapy. Such infections may contribute to sperm damage and is easily treatable.
Semen Analysis – Conclusion
It is important to note that, even though normal ranges are given for various sperm parameters, these do not separate clearly between infertile and fertile semen. Couples with male factor infertility have a reduced chance of pregnancy. Nonetheless, even in couples with a sperm count of less than 5 million per millilitre, approximately 25% of couples achieve a pregnancy within a two-year period. Such data shows that sperm count is only an imprecise measure of male fertility. A man cannot generally be said to be sterile when moving sperm are present in the ejaculate. Factors including the duration of infertility, the frequency and timing of intercourse, and the age and health of his partner are all important factors in the equation.
Despite its deceptive simplicity, routine semen analysis requires attention to detail to maximise its diagnostic usefulness. It is also a valuable tool in discussing the likelihood of spontaneous pregnancy over a given period of time and/or the possible need for assisted reproduction.