A fertile sperm has certain characteristics that enable it to fertilize an egg. Understanding what makes a sperm fertile is important for assessing male fertility and improving chances of conception.
What is a sperm cell?
Sperm cells, also known as spermatozoa, are the male reproductive cells. They are produced in the testes and transported through a system of ducts and glands where they mature and become capable of fertilizing an egg.
Sperm cells have a head, midpiece, and tail. The head contains the genetic material (DNA) needed to fertilize an egg. The midpiece contains mitochondria that provide energy for motility. The tail enables mobility and propels the sperm towards the egg.
What makes a sperm fertile?
For a sperm to be considered fertile, it must have normal structure, good motility, and effective metabolism to penetrate an egg and deliver DNA.
Normal structure
A fertile sperm should have proper development of the head, midpiece, and tail. Defects can impair function.
- Head – carries genetic material and enzymes to penetrate egg. Normal shape and size.
- Midpiece – contains mitochondria for energy. Right length and attachment to head.
- Tail – provides motility. Should be long enough with uniform structure.
Good motility
Sperm motility refers to its ability to move properly. Fertile sperm should display:
- Progressive motility – active linear movement
- Rapid speed – at least 25 micrometers per second
- Propulsion – powerful tail with effective flagellar movement
Low motility can prevent sperm from reaching and penetrating the egg.
Effective metabolism
The sperm must have the metabolic capacity to survive, mature, and fertilize. This depends on:
- Mitochondria – produces energy for movement
- Enzymes – needed to penetrate egg
- Membranes – regulates proper function
- DNA – genetic material to combine with egg
Abnormalities in any metabolic components can impair fertility.
What does a fertile sperm look like?
Under a microscope, a fertile sperm should display:
- Oval-shaped head – Length about 4-5 μm, width 2-3 μm
- Regular, smooth margins – No large vacuoles or irregularities
- Single tail – About 50 μm long, uniform along entire length
- Thin midpiece – About 1 μm wide and 5-10 μm long
- Clear acrosome – Cap-like structure covering 2/3 of head
- No residual cytoplasm – Indicates maturity
- No defects – Such as double heads or bent/coiled tails
Here is a diagram of a normal fertile sperm:
Image source: VeryWell Health
Key statistics on fertile sperm
Here are some key statistics on what defines a fertile sperm (WHO reference values):
| Feature | Fertile sperm |
|---|---|
| Sperm concentration | > 15 million/mL |
| Total sperm number | > 39 million per ejaculate |
| Motility | > 40% progressive motility |
| Morphology | > 4% normal forms |
| Volume | ≥ 1.5 mL |
| pH | ≥ 7.2 |
| Vitality | > 58% live |
Sperm counts and quality below these thresholds may indicate subfertility.
What affects sperm fertility?
Many factors influence sperm fertility including:
Genetics
– Abnormal chromosomes
– Gene defects – e.g. cystic fibrosis gene
Health conditions
– Varicocele – enlarged veins in scrotum
– Infections – mumps, HIV
– Sexually transmitted infections
– Epididymitis – inflammation of epididymis ducts
– Obesity
– Diabetes
– Thyroid problems
Lifestyle factors
– Drug use – anabolic steroids, opioids
– Heavy alcohol use
– Smoking
– High stress levels
– Exposure to chemicals/toxins
– Overheating testicles – hot baths, tight clothes
– High intensity exercise
Environmental factors
– Pollution
– Radiation or electromagnetic fields
Age
– Sperm quality declines with age
How is sperm fertility tested?
Sperm fertility is assessed through semen analysis. This involves evaluating:
- Count – Total number of sperm. Lower than 15 million/mL is suboptimal.
- Concentration – Number of sperm per milliliter of semen. Should be at least 15 million/mL.
- Motility – Percentage of moving sperm. At least 40% should have progressive motility.
- Morphology – Percentage of sperm with normal shape/form. Over 4% is considered normal.
- Volume – Amount of semen per ejaculate. Should be at least 1.5 mL.
- pH – Acidity level of semen. Normal is between 7.2-8.0.
- Vitality – Percentage of live, membrane-intact sperm. Should exceed 58%.
DNA fragmentation testing may also be done to assess sperm genetic integrity.
How to improve sperm fertility
If sperm quality is poor, here are some ways to improve fertility:
- Avoid tobacco, excess alcohol, drugs
- Exercise moderately
- Get BMI into normal range
- Reduce stress with meditation, yoga
- Take antioxidants – vitamin C, E, selenium
- Take supplements – zinc, CoQ10, folic acid
- Eat healthy – fruits, vegetables, whole grains
- Avoid overheating testicles
- Treat infections properly
- Get appropriate medical care
It takes about 3 months for lifestyle changes to improve sperm quality since they have a development cycle of around 74 days.
Medical treatments
If lifestyle remedies are insufficient, medical therapies that may help include:
- Surgery to repair varicocele
- Hormone therapies
- Assisted reproductive techniques – IVF, ICSI
Seeking timely medical care is important for dealing with any underlying health conditions impairing fertility.
Conclusion
Fertile sperm have normal structure, high motility, and effective metabolism to successfully fertilize an egg. Key parameters like concentration, morphology, and vitality should meet WHO reference thresholds.
Subfertility arises from genetic defects as well as health, lifestyle, and environmental factors. Improving sperm quality involves optimizing these parameters and seeking appropriate medical treatment if required.
Understanding the characteristics of fertile sperm is important for assessing male reproductive health and supporting conception.