Sperm Morphology: FAQ on Sperm Size and Shape

One of the important criteria that are assessed during a semen analysis is sperm morphology (the others are count, motility and volume). Sperm morphology is the term used to describe the appearance (size and shape) of sperm. We will often have patients worried because the sperm morphology is “low” (teratospermia). While there are some things that can be done to improve sperm morphology, whether or not they will work depends on the cause of the abnormality and whether it is genetic or environmental.

What is normal sperm morphology?

Morphologically normal human sperm will have a head with a normal acrosome (cap), a midpiece, and a long tail. Sperm is described as normal if:

1. it has a smooth oval-shaped head that is 5 to 6 micrometers long and 2.5 to 3.5 micrometers wide
2. A well-defined acrosome (cap) covering 40 to 70 percent of the head.
3. No visible abnormality of neck, midpiece, or tail.
4. No fluid droplets (vacuoles) in the sperm head that are bigger than one half of the sperm head size.

What are some common abnormalities in sperm?

There are many abnormalities that can be seen in a sperm, which include head and tail defects. These defects can be abnormally large heads, round heads, pin heads, crooked tails, and/or missing acrosomes. The whip like motion of the tail is what propels the sperm forward to swim through the passages of the female reproductive system towards the egg. If abnormal sperm has a defective tail it will have a very difficult time reaching the egg and fertilizing it. Head defects can also interfere with fertilization. The egg is enclosed in a glycoprotein coat called the zona pellucida (ZP). The ZP can be viewed as a filter for morphologically normal sperm because it has been shown that sperm with abnormal head morphology attach to the ZP in lower frequencies than sperm that have normal head morphology.

How is sperm morphology assessed?

Sperm morphology evaluation is a component of a complete semen analysis. Sperm cells are stained to make them visible, and several hundred are viewed under high magnification and scored individually as normal or abnormal based on their shape and size. The percentages of normal and abnormal shaped cells are calculated. In a typical sample of a man considered to have a normal, healthy semen sample, we would expect to see more abnormal sperm cells than normal.

What is “normal” sperm morphology?

Sperm morphology is assessed using one of 2 sets of characteristics. Kruger criteria are “strict” and consider minute irregularities as abnormal. Using these criteria, men with 4% normal sperm are considered to have normal sperm morphology. World Health Organization (WHO) criteria are more lenient and do not classify as many sperm as abnormal. Based on WHO criteria, men with 30% normal sperm are considered to have normal sperm morphology.

What are the causes of abnormal morphology?

There are many factors that can lead to formation of abnormal sperm. The common ones are genetics, exposure to toxic chemicals, increased testicular temperature and infection.

Can morphologically abnormal sperm fertilize an egg?

Yes. However, men with low morphology have been shown to have infertility in some studies. Usually, low morphology is associated with low sperm count or motility. Men with low morphology may also have no trouble causing a pregnancy.

Will eggs fertilized with abnormally shaped sperm increase the risk of having a child with genetic abnormalities?

We don’t know the answer to this question. There is no relationship between the shape of a sperm and its genetic material. Once the sperm enters the egg, fertilization has a good chance of taking place. However, as some of the abnormalities in sperm shape may be the result of genetic disturbances, there may be some male offspring who will inherit the same type of morphology abnormalities as are found in the father’s sperm morphology.

Does shape really matter?

Men with low sperm morphology can have trouble getting their partners pregnant. We, however, do not know if the cause of infertility was the shape itself or by another reason that causes the sperm to be shaped differently and at the same time causes a problem with fertility. A recent publication showed no difference in pregnancy rates with intrauterine inseminations based on morphology.

What can be done to improve morphology?

Nothing can be done if it is a genetic trait; however, the other causes may be reversible. Spermatogenesis takes place at a lower temperature than the overall body temperature. Anything that increases the testicular temperature e.g. wearing tight clothes that hold the testes close to the body will cause the production of abnormal sperm. Leading a healthy lifestyle, such as not smoking and reducing the amount of alcohol consumed, may also help.

Are there any dietary supplements or vitamins that I can take to improve morphology or fertility?

Dietary supplements or vitamins have not been shown to improve sperm morphology or fertility. Some specialists recommend that you take a daily multivitamin to improve reproductive health even though the value of dietary multivitamins for this purpose is unproven.

To see a fertility specialist who covers the full range of female and male fertility issues, schedule an appointment at one of InVia's four Chicago area fertility clinics.