Sperm Morphology (Size and Shape)

Sperm morphology overview

  • Sperm morphology refers to the size, shape and appearance of a man’s sperm, which when abnormal can decrease fertility and make it more difficult to fertilize the woman’s egg.
  • Sperm can be misshaped based on the size of the head, having an extra head, and having no head or tail. Other sperm defects include bent tail, coiled-tail, stump-tail and not having the tail attached at the correct location.
  • For a sperm sample to be considered to have fertility potential, it only needs 4 percent or more of the sperm population to be considered normal, using the “strict” morphology criteria.
  • Some couples will need to use IUI, IVF or ICSI to improve their chances of becoming parents based on the sperm morphology results.

What is sperm morphology?

Sperm morphology refers to the shape of the sperm, which includes head size and head DNA content (revealed by a nuclear color stain), the midpiece appearance and the structure of the tail. The head shape is important because it can affect the sperm’s ability to penetrate the outer surface of a woman’s egg to fertilize it.

Sperm morphology is assessed during routine semen analysis that examines the sperm cells under a microscope. The semen analysis will also examine the motility (movement ability) and concentration of sperm present.

Every male, fertile or infertile, has varying percentages of abnormally-shaped sperm. There are many factors that can lead to abnormally shaped sperm including increased testicular temperature, exposure to toxic chemicals, infection and genetic traits. The medical term for when a man has a large number of abnormally shaped sperm is teratozoospermia or teratospermia.

Loma Linda Center for Fertility & IVF uses the Kruger Strict Criteria to evaluate sperm morphology, which is used by most doctors. Below are the Kruger Strict Criteria scores and their explanations:

  • Over 14 percent of sperm have normal morphology – high probability of fertility
  • 4-14 percent – fertility slightly decreased
  • 0-3 percent – fertility extremely impaired.

The World Health Organization also published their own sperm analysis criteria. As of 2010, they consider the presence of 4 percent and higher of sperm having normal morphology as the ideal sample composition for fertility.

Types of sperm morphology

Sperm morphology | LLU Center for Fertility & IVF | Normal sperm
Normal-shaped sperm
A normal sperm will have an oval-shaped head, an intact midpiece and an uncoiled single tail. Sperm with normal morphology are able to swim well and in a straight line. Normal sperm will also contain healthy genetic information rather than having too many or too few chromosomes, which are common in abnormally shaped sperm.

Sperm morphology | LLU Center for Fertility & IVF | Macrocephaly sperm
Macrocephaly sperm
Macrocephaly refers to when the sperm has a giant head. These types of sperm often carry extra chromosomes and have problems fertilizing the woman’s egg. Macrocephalic sperm may be caused by homozygous mutation of the aurora kinase C gene. This means that because this kind of sperm abnormality may be genetic, fathers may be able to pass the condition on to their sons.

Sperm morphology | LLU Center for Fertility & IVF | Small head sperm
Microcephaly, or small-head sperm
Microcephaly is when the sperm’s head is smaller than normal, also known as small-head sperm. Small-head sperm may have defective acrosome (a pocket of enzymes in the sperm head used to enter the egg) or reduced genetic material.

Sperm morphology | LLU Center for Fertility | pinhead sperm
Pinhead sperm
Pinhead sperm, a variation of the small-head sperm, is when the head appears as a pin with minimal to no paternal DNA content. The presence of pinhead sperm may point to a diabetic condition.

Sperm morphology | LLU Center for Fertility & IVF | Tapered head sperm
Tapered head sperm
Tapered head sperm are sperm with “cigar-shaped” heads that may indicate the presence of varicocele in the male or constant exposure of the scrotum to high temperature locations such as daily hot sauna. These tapered head sperm often contain abnormal chromatin or packaging of the paternal DNA genetic material. Abnormal number of sperm chromosomes called aneuploidy has been shown in tapered head sperm.

Sperm morphology | LLU Center for Fertility & IVF | Thin sperm
Thin head sperm
An extreme variation of the tapered head sperm is the “thin narrow” head sperm with pathologies seemingly different from the tapered head sperm. Thin head sperm are seldom identified and they may be due to broken DNA, varicocele or disrupted head formation.

Sperm morphology | LLU Center for Fertility & IVF | Decondensing head sperm
Decondensing head sperm
Globozoospermia, or round headed sperm condition, is an abnormal sperm morphology that indicates either there is an absence of the acrosome or the sperm is missing inner parts of its head responsible for “activating” or turning on the egg and starting the fertilization process. A variation of this type of sperm is the Decondensing head sperm seen when the sperm prematurely starts to break down its nucleus and the unraveling DNA material fills the entire sperm head.

Sperm morphology | LLU Center for Fertility & IVF | Headless sperm
Headless sperm
Headless sperm have no head at all and are called acephalic sperm or decapitated sperm syndrome. They do not have genetic material or chromosomes. This type of sperm may look like a pinhead sperm but upon close examination, one can see that there is no tiny sperm head giving the sperm the appearance of a loose piece of string.

Sperm morphology | LLU Center for Fertility & IVF | Acaudate sperm
Tail-less sperm
Tail-less sperm are called acaudate sperm, and these sperm are often seen during necrosis, the death of most or all of the cells in an organ.

Sperm morphology | LLU Center for Fertility IVF | Nuclear vacuoles sperm
Nuclear vacuoles sperm
Nuclear vacuoles sperm have two or more large vacuoles (cyst-like bubbles) or multiple small vacuoles in the sperm head. These nuclear vacuoles are visible under high magnification microscopy. While some studies show this type of sperm has low fertilization potential, other studies have shown no effect. Studies are still in progress.

Sperm morphology | LLU Center for Fertility & IVF | Multi head sperm
Multi-head sperm
Multiple parts sperm can have multiple heads or tails. When the sperm has two heads, it is called a duplicate sperm, a condition linked to exposure to toxic chemicals, heavy metals like cesium, smoke or high prolactin hormone in the male.

Sperm morphology | LLU Center for Fertility & IVF | thick neck sperm
Thick, swollen neck
Large swollen midpiece or sperm neck may be related to defective mitochondria, the energy-making parts of the sperm cell. It may also be a sign that the centrioles, the guidance system for moving chromosomes stored at the sperm neck, may be missing or broken.

Sperm morphology | LLU Center for Fertility & IVF | Coiled tail sperm
Coiled-tail sperm
Coiled-tail sperm have been exposed to either incorrect seminal fluid conditions or the presence of bacteria. These sperm cannot swim, as their tails are damaged. Heavy smoking has been linked to the presence of coiled-tail sperm.

Sperm morphology | LLU Center for Fertility | stump tail sperm
Stump tail sperm
Sperm cells with short tails often have low or no motility and are called stump tail or Dysplasia of Fibrous Sheath (DFS) sperm. This tail defect happens during late spermiogenesis or sperm cell formation in the testis. Some patients with DFS also have chronic respiratory disease associated with immotile cilia syndrome. Stump-tail or DFS is an autosomal recessive genetic disease connected with abnormal genes that encode for proteins such as the sperm neck centrin 1 protein. DFS has been linked to a higher percentage of sperm aneuploidies or abnormal chromosomes.

Sperm morphology’s effects on fertility

While the most common cause of male infertility is low sperm count, the shape of the sperm can also play a role. Morphology can affect fertility because sperm need a certain shape to be able to penetrate the outer layers of the egg.

Most men with abnormal sperm morphology are still able to father a child, but achieving pregnancy may take longer or require assistance from a fertility specialist.

Intrauterine insemination (IUI) or in vitro fertilization (IVF) may be an option for those with sperm morphology issues. Intracytoplasmic sperm injection (ICSI) can be used in addition to IVF to increase the chances. Taking antioxidants in male fertility supplements for three or more months has been shown by some researchers to improve abnormal sperm morphology.

During IVF with ICSI, the lab will be able to choose a sperm that has the highest chance of success, based on morphology and motility, and directly inject the sperm into a woman’s egg. Once the sperm and egg combine to make an embryo, it will be implanted into the woman’s womb at the right stage of development.

Sperm morphology is just one of many factors affecting male fertility. Find out about other causes of male infertility.

Can sperm shape be corrected?

A man’s body is always producing new sperm. As he ages, his sperm can become less healthy. For most men, sperm production will begin to drop after age 40. Changes to a man’s diet and lifestyle that can improve the health of future sperm include:

  • Exercising regularly
  • Avoiding self-medicated testosterone steroid use, heavy tobacco use, drinking or illegal drugs
  • Reducing the amount of caffeine consumed
  • Losing weight, if needed
  • Avoiding hot tubs
  • Decreasing stress
  • Wearing loose, cotton boxer shorts
  • Eating foods or supplements rich in antioxidants every day.

Note that it takes about three months to make and transit the new sperm, so any changes in diet or lifestyle will require some time before improvements are seen. Due to the effects of aging, some physicians will recommend that a man freeze his sperm earlier in life if he expects he will be waiting until later in life to have a child. This allows a man to have the healthiest sperm available when looking to start a family at any age. The sperm freezing and banking process works best only when the man has adequate normal healthy sperm.

For more information about male fertility, make an appointment to meet with a physician at the Loma Linda University Center for Fertility and IVF.
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