Poor sperm count (oligospermia) is described as is one cause of male infertility. Although it takes only a single sperm to fertilize an egg (ovum), the odds of a single sperm reaching the egg are very low. A normal sperm count is 20 million or more sperm per milliliter of semen. In order to father a child, at least 60 percent of those sperm should have a normal shape and show normal forward movement (motility).

Poor morphology is one of the least predictable numbers in the semen analysis, and basically describes the percentage of sperm that look normal. There are two methods used to describe normal and abnormal sperm. Firstly, the WHO method provides quite a critical analysis of the sperm. The other, known as Kruger morphology, involves a more in-depth description of what determines a "normal-appearing" sperm. While the WHO believes that sperm are viable when only 40% are normal, Kruger analysis believes that only 15% normal are needed for a reproduction.

These tests have their critics though, and it is believed in some quarters that they have little predictive value in identifying those for whom fertility treatment will be effective. (Perloe, M (n.d.)) This discrepancy in classification has come about as the WHO classifies sperm on the borderline of normality as 'normal', whereas the Kruger system classifies them as 'abnormal', and by classifying conservatively, they apparently increase the chances of successfully predicting the sperm's ability to fertilise an egg. In the 21st century, the Kruger system is used far more in modern clinics to determine the feasibility of sperm.

A sperm morphology score is usually determined during the course of a semen analysis, and it is this which allows doctors to make an assessment and direct the patient toward an appropriate treatment. This is done by preparing a microscope slide with a very thin coating of semen. The slide is then stained to make the sperm clearly visible, and several hundred sperm are viewed under high magnification and individually scored 'normal' or 'abnormal' based on their shape. The percentage of normally shaped sperm is then calculated.

Based on results from in vitro fertilization studies where a fixed number of sperm were used to inseminate each egg, when the percentage of normally shaped sperm dropped below 14%, fertilization began to decline. When the percentage of normally shaped sperm dropped below 4%, fertilization was very poor or non-existent.

The shape of a sperm is an important factor in determining how well it is able to fertilise an egg. The egg is enclosed in a protein coat called the zona pellucida (ZP) which performs many functions, the first of which is to select which sperm will fertilise the egg. The ZP bases its selection on the shape of the sperm head, so in order to pass through the ZP, the sperm must be vigorously motile and the sperm head must be a symmetrical, oval shape of the appropriate size. Sperm possessing heads that are irregular in shape, too round, too long, too big or too small are prevented from passing through the ZP.

Sperm motility is determined by the percentage of sperm that are moving and qualified by the sperm's capacity to swim in a sustained, forward direction. Healthy sperm motility is the critical attribute that allows sperm to propel themselves through the uterus to the fallopian tube, penetrate the surface of the ovum, and fertilize the egg.

Smoking marijuana has a profound effect on sperm motility - causing them to 'burn out' as although their initial swimming capabilities remain undiminished, the hyperactivation (final push required from sperm to enter the egg) was significantly impaired.

However, if motility is affected, one cup of coffee per day can have a positive effect. This must be very carefully differentiated from problems with sperm count or morphology, as caffeine in these cases can be detrimental.

Sperm autoimmunity is a condition that accounts for about 6% of male infertility. The immune system produces antibodies as part of the normal defense 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.

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).