What is Sperm Morphology and how does it affect male fertility?
The classification individual sperm based on size and shape is known as Sperm Morphology. The sperm is the smallest cell in the human body, about 5 x 3 micrometers in size, excluding the tail. The sperm consists of 3 regions – the head, neck-midpiece and tail. The anterior half of the head is covered with an acrosome
which is like a cap and helps the sperm to penetrate the protective membrane of the female egg and allow fusion of the two.
All of an individual’s sperm may not look exactly alike. There may be changes in sperm size and shape and these can occur in any or all of the 3 parts. In normal sperm, the head is oval in shape, the midpiece slender and the tail long. Abnormal sperm may have defects, such as a large or round head or a bent or very thin neck or a short, crooked or coiled tail. In some cases, due to these mutations or defects, the sperm may not be able to move correctly or with enough speed to reach and enter the egg’s membrane, which can sometimes be a cause for infertility.
Sperm morphology is usually assessed during a routine semen analysis test, where the amount and quality of sperm present in the semen can be estimated under various heads – semen volume, total sperm count, sperm concentration, vitality and motility. The medical names for these various conditions are:
- Teratozoospermia (or Teratospermia) – a condition where there is abnormal sperm morphology which affects fertility in males.
- Oligospermia shows a low sperm count and
- Asthenozoospermia (or Asthenospermia) means reduced sperm motility.
A patient is always advised to have at least 3 semen analysis done before coming to any conclusion on the quality of their semen sample, as semen samples are known to be prone to highly variability depending on the physiological and psychological state of the patient. Hence, an average of 3 such semen analysis reports is taken and assessed by a Clinician to get an accurate diagnosis on the semen sample of the individual. While the actual range can vary, normally, a healthy sperm morphology range is between 4 and 14 percent. A reading of below 4 percent is termed abnormal and may just mean that it will take longer than normal to conceive, in some cases.
However, we must remember that a semen analysis only analyses the external characteristics of the sperm and does not give an indication of the quality of the internal genetic material. To provide a more accurate assessment of sperm quality, more specialized tests including sperm DNA fragmentation (SDF) and reactive oxygen species (ROS) are carried out. The integrity of sperm DNA is essential for fertility and some causes for DNA fragmentation are lifestyle factors, including smoking, excessive alcohol, cell phone radiation, obesity, age or sedentary occupations.
With the newer DNA tests and increased technology as in the SCSA (Sperm Chromatin Structure Assay) test, which is an advanced test for male infertility, it has been proven that even though some men have low sperm morphology, it is possible to try other methods, like the ICSI (intracytoplasmic sperm injection) where a morphologically normal sperm from a semen sample is injected into an egg) to overcome this problem.
There has been a downward trend over the years in the reported values of normal sperm morphology by the WHO. About 20 years ago, 15% was considered normal and now, in the 2010 edition, that number has dropped to 4%. This is due to several factors, one of the main being the strict criteria now introduced for evaluating sperm morphology. Others may include negative environmental influences which suggest a decrease in semen parameters.
Although Sperm Morphology evaluated with such criteria, on its own, may not provide the complete diagnosis for male infertility, it still plays a very important role in the evaluation of the same and it should be used with other parameters to determine clinical implications.