Sperm Morphology: What Is It and Why Is It Important?

Sperm morphology refers to the physical appearance of sperm, including their size and shape.

Key Takeaways:

• Doctors often examine sperm morphology, along with other factors such as sperm count, sperm motility, and overall semen quality, when assessing fertility.

• Abnormal sperm morphology has many potential causes, including testicular damage, lifestyle factors, and genetic factors.

• Fertility treatments such as IUI, IVF, or ICSI can help men with fertility problems conceive a child if they aren’t able to through vaginal sex alone. 
  

A sperm cell has its work cut out for it when it comes to fertilizing an egg. It has to compete against millions of other sperm, race through an acidic vagina, and then reach the egg and penetrate its outer layer.

Sperm morphology is a measure of the size and shape of sperm. It’s one of the key factors that help determine a sperm’s chances of successful fertilization. If lab analysis shows that you have a higher-than-normal number of sperm with abnormal morphology, you may have difficulty conceiving.

The good news is that making lifestyle changes can often improve sperm morphology, and there are now many modern fertilization treatments available to help aid reproduction.

Read on for a deeper look at sperm morphology, including what factors influence morphology, how to increase sperm morphology, and what fertilization treatments are available.

Semen usually contains more than 39 million sperm each time you ejaculate. Your sperm count is considered low if your semen sample contains fewer sperm than this.

With so many sperm circulating, it’s normal for a certain percentage of sperm to have abnormalities. In fact, the World Health Organization (WHO) now considers you to have normal sperm morphology even if only 4 percent of your sperm are free from defects, as this is the bottom of the normal range. Men who reach this threshold usually don’t have problems or only have minimal problems conceiving unless they have other sperm or semen issues. 

The two main parts of sperm morphology are the size and shape of sperm, which are assessed by healthcare professionals from a semen sample.

The WHO recommends testing sperm morphology as a part of routine semen analysis when assessing male fertility.

Keep reading to learn the typical shape of sperm and some abnormalities that can develop.

The Head Structure

The sperm head contains the chromosomes and highly condensed genetic material that eventually makes up half the DNA of a fetus.

What does healthy sperm look like? A normal sperm head should have:

• A smooth appearance

• Oval shape

• An acrosome, a region on the head that makes up 40–70 percent of the total area and attaches to the egg

• No large vacuoles (holes) or no more than two small vacuoles

Some abnormalities that can develop in the sperm head include:

• Pinhead sperm (tiny or undeveloped heads)

• Double heads

• Globozoospermia, or round-headed sperm without an acrosome

• Irregular or elongated shape

• Large vacuoles

• Poor DNA integrity

The Midpiece

The midpiece contains tightly packed mitochondria that fuel sperm motility. Mitochondria are small structures that supply your cells with energy.

Problems that can develop with the midpiece include:

• Abnormal, asymmetrical, or bent shape

• Overly slender 

• Excess cytoplasmic residue, which is material from development that can make sperm slower

The Tail

A sperm’s tail helps it swim through fluids, similar to the tail of a tadpole. Normal tails are straight, flexible, and long. Tail defects can include:

• Short tails

• Bent tails or tails with sharp angles

• Coiled tails

• Multiple tails

Having a higher-than-normal number of improperly formed sperm is known as abnormal sperm morphology, or medically as teratozoospermia. It can result from numerous biological, environmental, and lifestyle influences.

Genetics

Many genetic conditions are linked to problems with fertility or abnormal sperm production. Your doctor may recommend genetic testing if 100 percent of your sperm show some type of structural abnormality, suggesting that the issue is being coded by a certain gene.

For example, AURKC mutations are associated with a large sperm head, or macrozoospermia, and DPY19L2 mutations are associated with round-headed sperm, or globozoospermia.

Environmental and Lifestyle Factors

Some environmental or lifestyle factors have been identified as causes or potential causes of abnormal sperm morphology or reduced fertility, including: 

• Exposure to air pollution

• Exposure to pesticides, industrial toxins, and other toxic chemicals

• Heat exposure to your testicles, such as through saunas and hot tubs

• Excessive alcohol consumption

• Possibly: smoking, cannabis use, and recreational drug use 

• Possibly: obesity

Medical Causes

Some medical conditions can affect the development of sperm and lead to abnormal morphology, such as:

• Varicocele, a common cause of male infertility characterized by swollen veins in your scrotum

• Low testosterone

• Other hormonal abnormalities, such as differences in thyroid-stimulating hormone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), or anti-Mullerian hormone

• Infections that produce inflammation in the reproductive system

The main way that doctors assess sperm morphology is by looking at a semen sample under a special microscope. Typically, they’ll analyze two semen samples obtained at least 4 weeks apart after abstaining from sexual activity for 2–7 days. 

Lab technicians then analyze sperm morphology by putting a small portion of semen on a glass slide and staining it with a special dye to make individual sperm easier to see under the microscope.

They’ll look for various abnormalities such as:

• Changes to the shape of sperm

• Acrosome size

• Presence of vacuoles

• Tail symmetry

• Overall proportions

Other fertility tests on semen samples may include looking at:

• Sperm concentration (sperm count)

• Sperm motility

• Volume

• pH

• Viscosity

Many factors can contribute to abnormal sperm morphology. It may be possible to improve morphology by treating underlying medical conditions or making lifestyle changes.

Lifestyle changes you can make that may improve sperm quality include:

• Eating a balanced diet

• Avoiding recreational drug use

• Reducing stress

• Avoiding pesticides

• Maintaining a healthy body weight

• Reducing alcohol consumption

• Eliminating tobacco use

• Wearing loose-fitting underwear and avoiding sources of heat to your testicles, such as hot tubs

• Getting plenty of sleep

Treatments for underlying medical conditions might include:

• Antibiotics for bacterial infections

• Hormonal therapy for imbalances

• Varicocele repair

Doctors often prescribe testosterone replacement therapy to men with low testosterone, but TRT can affect fertility. For men planning on having children, doctors often recommend other medications to increase their body’s production of testosterone, such as enclomiphene or human chorionic gonadotropin (hCG). 

Learn more about increasing testosterone without affecting your fertility. 

If your doctor tells you that you have a lower-than-normal number of sperm with normal morphology, you may worry about what this means for your fertility if you’re planning on having children.

Many men with low morphology can still father children naturally. Sperm morphology alone is not a strong predictor of fertility unless coupled with very low sperm count or poor sperm motility.

Humans seem to produce a high number of abnormal sperm compared to other animals. Unless you dip below the WHO’s cutoff of 4 percent, it may not significantly affect your chances of having children. If abnormal sperm morphology does make it more difficult to conceive naturally, there are alternative methods available.

Intrauterine Insemination (IUI)

IUI is a fertility treatment where sperm is injected directly into a woman’s uterus.

Success in IUI depends more on the number of motile sperm than on morphology alone. As long as sperm concentration and motility are adequate, abnormal morphology may not affect IUI outcomes.

In Vitro Fertilization (IVF)

IVF is a procedure where eggs are fertilized by sperm in a lab. Then, a fertilized embryo is implanted in a woman’s uterus.

In IVF, sperm morphology plays a limited role because fertilization occurs in a controlled environment. Embryologists can select the healthiest-looking sperm for insemination.

Intracytoplasmic Sperm Injection (ICSI)

In cases of severe morphological abnormalities, clinics often use ICSI, an advanced form of assisted reproductive technology. This technique involves directly injecting a sperm into an egg.

During ICSI, a single sperm is injected directly into the egg, bypassing issues with structure or motility.

Sperm morphology is a measure of the physical appearance of sperm. The main parts of sperm morphology are the size and shape.

Understanding sperm morphology can help doctors identify potential fertility problems. Most cases of abnormal sperm morphology can be managed effectively, offering hope to people pursuing parenthood.

Making an appointment with a fertility specialist can help you understand your options. They can walk you through the best infertility treatments for your situation and talk to you about the pros and cons of each. 

What does a normal sperm look like?

A normal sperm has a smooth, oval-shaped head with a section called the acrosome that allows it to bind to an egg. It also has a thin, well-aligned midpiece and a single long, straight tail.

Can you improve sperm morphology?

Lifestyle factors can contribute to the development of healthy sperm. Some ways you may be able to improve sperm morphology include eating a balanced diet, getting regular exercise, avoiding smoking and excessive alcohol use, and limiting how much heat your testicles are exposed to.

Does morphology matter in IVF or ICSI?

Morphology matters less for IVF or ICSI than it does for conceiving naturally. In ICSI, morphology issues are largely bypassed because the sperm is directly injected into the egg, making it highly effective for severe abnormalities. During IVF, healthcare professionals can select the healthiest-looking sperm for fertilization.