A semen analysis evaluates certain characteristics of a male’s semen and the sperm contained in the semen. An analysis is performed when investigating a couple’s subfertility or after vasectomy to verify that the procedure was successful.
The characteristics measured by semen analysis are only some of the factors determining semen quality. It is important to understand that it is the function of the sperm that is important rather than the actual numbers in a report and that the interpretation of the result must take into account the entire assessment of a couple and their wishes and expectations. It is known 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.
Examples of parameters measured in a semen analysis are sperm count, motility and morphology.
Sperm density or sperm concentration measures the concentration of sperm in a man's ejaculate. Over 15 million sperm per milliliter is considered normal, according to the World Health Organisation (WHO) in 2010. Older definitions state 20 million per ml. A lower sperm count is considered oligospermia. A vasectomy is considered successful if the sample is azoospermic. The average sperm count today is around 60 million per milliliter in the Western world, having decreased by 1-2% per year from a substantially higher number decades ago.
Sperm motility describes the movement of the sperm. Motility is divided into four different grades:
- Grade 1: Sperm with progressive motility. These are the strongest and swim fast in a straight line.
- Grade 2: (non-linear motility): These also move forward but tend to travel in a curved or crooked motion.
- Grade 3: These have non-progressive motility because they do not move forward despite the fact that they move their tails.
- Grade 4: These are immotile and fail to move at all.
Some authorities define normal motility as 60% of observed sperm, or at least 8 million per ml, showing good forward movement. The WHO has a similar value of 32% 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 15 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 ml. The other way around, a man can have a sperm count far less than 20 million sperm cells per ml and still have good motility, if more than 60% of those observed sperm cells show good forward movement.
The morphology of the sperm is also evaluated. With WHO criteria as described in 2010, a sample is normal (samples from men whose partners had a pregnancy in the last 12 months) if 4% (or 5th centile) or more of the observed sperm have normal morphology.
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 a lower frequency of aneuploidy.
WHO regards 1.5 ml as the lower reference limit. Low volume may indicate partial or complete blockage of the seminal vesicles or that the man was born without seminal vesicles. In clinical practice, a volume of less than 2 mL in the setting of infertility and absent sperm should prompt an evaluation for obstructive azoospermia. A caveat to this is be sure it has been at least 48 hours since the last ejaculation to time of sample collection.
The level of fructose in the semen is measured. WebMD lists normal as at least 3 mg/ml. WHO specifies a normal level of 13 μmol per sample. Absence of fructose may indicate a problem with the seminal vesicles.
WHO criteria specify normal as 7.2-7.8. Acidic ejaculate (lower pH value) may indicate one or both of the seminal vesicles are blocked. A basic ejaculate (higher pH value) may indicate an infection. A pH value outside of the normal range is harmful to sperm.
The liquefaction is the process when the gel formed by proteins from the seminal vesicles is broken up and the semen becomes more liquid. It normally takes less than 20 minutes for the sample to change from a thick gel into a liquid. An abnormally long liquefaction (more than 30 minutes at 37 24°C) time may indicate an infection. In the NICE guidelines, a liquefaction time within 60 minutes is regarded as within normal ranges.
- Aspermia: absence of semen
- Azoospermia: absence of sperm
- Hypospermia: low semen volume
- Oligospermia: low sperm count
- Asthenozoospermia: Poor sperm motility
- Teratozppspermia: sperm exhibit more morphological defects than usual