Definition - What does Non-Motile Sperm mean?
Non-motile sperm are sperm cells that have completely lost their ability to rhythmically swing its tail and move constantly in a forward direction due to a structural or functional defect of the sperm. Once deposited in the vagina, sperm need to actively move across the vagina and uterus to the fallopian tubes to meet with an egg for fertilization and for successful conception, more than 50% of the sperm in semen needs to have normal motility. Having a higher percentage of non-motile sperm in semen decreases the chances of successful fertilization of the egg and is a known cause of male factor infertility.
FertilitySmarts explains Non-Motile Sperm
Sperm need to travel a long distance from the vagina to the fallopian tubes to fertilize an egg, and out of the millions of sperm that are released into the vagina during intercourse and ejaculation, only a few are able to survive this journey. Being able to maintain a progressive forward movement through the reproductive tract is key to a successful fertilization.
Sperm can be classified into 5 groups based on their motility.
- Grade 0: Non-motile sperm. No motion at all.
- Grade 1: Some motion of sperm is present, but there is no forward movement.
- Grade 2: Sperm movement is slow and does not move in a straight line.
- Grade 3: Sperm can move forward but the speed is low or it cannot move in a straight line.
- Grade 4: Sperm can move forward at a steady speed in a straight line.
The tail of the sperm is the most important structure that determines the ability of sperm to be motile. Tail movements require a lot of energy, that is supplied by mitochondria in the sperm cell in the form of ATP. Any structural abnormalities of the sperm or an abnormality in sperm function or metabolism can impair sperm mobility.
Some of the common causes that can result in non-motile sperm include:
- Abnormalities of the male reproductive tract
- Genetic diseases (eg: cystic fibrosis)
- Sperm DNA abnormalities
- Exposure to chemicals (eg: chemotherapy) and toxins (eg: heavy metals)
- Environmental factors (eg: exposure of testicles to extreme heat, cold or radiation)
Sperm cells go through a cascade of cell division and maturation to achieve its final morphology and function. Sperm gain their full motility in the later stages of development that happens in the epidermis. During surgical retrieval of sperm through a needle, there is a higher chance of collecting premature sperm that are either non-motile or weakly motile. But studies have shown that sperm motility does not have a significant impact on the success rates of assisted reproductive technologies such as in vitro fertilization (IVF) and Intracytoplasmic sperm injection (ICSI).