During a natural pregnancy, a sperm has to swim all the way up the cervix, through the uterus into the fallopian tubes to find the egg. When a man has a low sperm count, it means there are fewer sperm to make this long journey, and hence it reduces the possibility of any sperm reaching the egg.
Even if some sperms do reach the egg, they may not be able to penetrate it the tough exterior of the egg. The result is the failure of sperm to fertilise the egg during ovulation period. Hence, fertilisation does not happen, and pregnancy is not achieved.
The ability of the sperm to move is referred to as sperm motility. For a man, his sperm count is important, but sperm motility is equally important. If you have a full load of sperm, but they are lazy and have limited motility, how are they going to travel to the egg.
In a semen analysis test, if at least 40% of the sperm are moving, it is considered normal sperm motility. This test records a movement based on the fact that the sperms are twitching their tails and wiggling about. However, for fertilisation, we need sperm to be able to move from one place to another. Wiggling in the same place will not suffice. Many sperms have limited motility, and their movement is restricted to the same spot.
Progressive motility is the ability of sperm to move from one place to another. When a man has sperm motility of 40%, he usually has progressive motility of 32%. This is considered normal and can easily make his female partner pregnant.
Another consideration of sperm motility is the direction they are swimming in. How many are swimming around in circles and how many are swimming straight? Those that are going around in circles are of no particular use for fertility. Those that are swimming straight have the potential to swim up to the female reproductive tract. A minimum of 12% of straight moving sperm is required for a successful pregnancy attempt. Less than 12% of straight moving sperm is considered poor sperm motility. If the progressive sperm motility of straight moving sperms is less than 12% the probability of the sperms reaching the female egg in time for fertilisation during ovulation, is minimal. A man requires above 12%of straight moving sperm for a normal and healthy sperm motility level and to be able to successfully impregnate his female partner.
Sperm motility is associated with sperm quality. If the sperm has poor motility, it results in male infertility. Couples who are not able to conceive due to sperm motility have a number of assisted fertility options that can help them to conceive successfully.
Intrauterine insemination is a procedure where the healthy sperm is injected directly into the uterus. This procedure saves the sperm the long journey from the cervix, making it easier by shortening the travel route. The IUI procedure is for males who have sperm motility of 30% to 40%. From the uterus, the sperms have to swim only a short distance to the fallopian tubes.
If the sperm motility is minimal and the IUI procedure is not successful, doctors suggest Intracytoplasmic Sperm Injection. The eggs are extracted from the female partner, and the sperm is directly injected into the egg. This technology is very successful, even if there is no sperm motility. The ICSI procedure has a successful fertilisation rate of around 80%. This technique is now popularly used for IVF treatment.