As fertility treatment has become more focused on the cellular level, important differences in sperm cells have become recognized as crucial to fertility.
Obviously, with the journey ahead of them toward uniting with an egg cell, the movement of sperm cells plays a large part in their ability to result in fertilization and conception. For natural, unassisted conception, a sturdy sperm cell will, after being deposited in the vagina, be able to swim through the cervix and into the fallopian tubes. The importance of sperm shape may seem less obvious, but reproductive scientists have learned through microscopic investigation that the outward shape of a sperm cell is often an indicator of its inner ability to perform the tasks at hand.
Motility refers to how the individual cells move. The term “total motility” is a numerical expression that describes the fraction of sperm that display any type of movement.
The highest quality sperm cells will move in a relatively straight path, rather than in a circle. Also, sperm must have the velocity to penetrate the zona pellucida, a hard outer coating of the egg, in order for fertilization to occur.
In an average semen analysis, total motility results will be listed on a zero to 100 percent scale. For average fertility, at least 50 percent of the sperm should be active. Their movement quality will be rated from zero to four, with a score of two being satisfactory.
Morphology refers to the shape of the sperm cell upon visual examination under a microscope.
A normal sperm cell will have an oval head with a long tail. Shape abnormalities — such as a very small, large or misshapen head, two heads, or a crooked or double tail — can prevent the sperm from being able to swim and/or fertilize the egg.
For a normal semen analysis result, at least 30 percent of sperm cells in a sample should be of normal shape according to the World Health Organization (WHO). Other analyses use what is called Kruger (strict) morphology parameters. Normal shaped heads should be visible in 14 percent or more of the viewed sperm for a normal result with Kruger parameters. Less than four percent normal shaped sperm could indicate a significant infertility problem.