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Infertility in Men


An in-depth report on the causes, diagnosis, treatment, and prevention of male infertility.

Sperm Abnormalities

More than 90% of male infertility cases are due to low sperm counts, poor sperm quality, or both. In 30% to 40% of cases of sperm abnormalities, the cause is unknown. It may be the end result of one or a combination of factors that include chronic illness, malnutrition, genetic defects, structural abnormalities, and environmental factors. Partial obstruction anywhere in the long passages through which sperm pass can reduce sperm counts. In one study, obstruction was believed to be a contributing factor in over 60% of low sperm count cases. Obstruction itself can be caused by many factors.

Defining Sperm Abnormalities

Sperm abnormalities are categorized by whether they affect sperm count, sperm quality, or both:


Medical Name

Description / Comment

Low sperm count


Generally defined as than 10 million sperm/mL of semen. There are literally dozens of causes of temporary and permanent low sperm count.

No sperm


Complete absence of sperm. This is relatively rare, affecting less than 1% of all men and 10% to 15% of infertile men. This may be due to obstruction or a failure to produce sperm in the testes, which can be caused by infections such as mumps, genetic disorders, radiation, or exposure to chemicals.

Low-quality sperm


Quality of sperm is determined by the following:

  • Its motility (its ability to move).
  • Its morphology (its shape and structure).

The quality of the sperm is often more significant than the count.

No semen production


Ejaculation does not emit any semen.

A large 2001 analysis, the most comprehensive to date, reported that the men most likely to be fertile had the following findings:

  • Sperm count. Men were most likely to be fertile with a sperm count over 48 million per milliliter of semen and least likely with counts below 13.5 million.
  • Sperm motility (movement). Men were most likely to be fertile when more than 63% of the sperm were moving and least likely with less than 32% sperm motility.
  • Sperm morphology (shape and structure). Men were most likely to be fertile when more than 12% of the sperm had a normal shape and structure and least likely when fewer than 9% of the sperm had a normal appearance.

Values between all these ranges constituted a sort of gray zone between fertile and infertile. The studys findings underline the important point that semen analysis is only one indicator of the ability to conceive a child. There was considerable overlap in all three values, and none of these figures, alone or combined, could diagnose infertility definitively.

Low Sperm Count

In the past, a sperm count of less than 40 million/mL in the ejaculate was believed to cause infertility. Now, however, if the woman is fertile and young, a count as low as 10 million can often accomplish conception over time, even without treatment. In fertilization clinics, men with low sperm counts report fertilization rates of about 30%, while those with average sperm counts have rates between 60% and 80%. Sperm count varies widely over time and temporary low counts are common. Therefore, a single test that reports a low count may not be a representative result.

Sperm Motility

Sperm motility is the sperm's ability to move. If movement is slow, not in a straight line, or both, the sperm have difficulty invading the cervical mucous or penetrating the hard outer shell of the egg. If 60% or more of sperm have normal motility, then the sperm is at least average in quality. If less than 40% of sperm are able to move in a straight line, the condition is considered abnormal. Sperm that move sluggishly may also have genetic or other defects that render them incapable of fertilizing the egg. An important 2001 study identified a protein in the tail of the sperm called CatSper, which might play a central role in the ability of the sperm to swim and penetrate the egg.

Sperm Morphology

Morphology refers to the shape and structure of an object. Morphology may be even more important than count or motility in determining potential fertility. Abnormally shaped sperm cannot fertilize an egg. About 60% of the sperm should be normal in size and shape for adequate fertility.

The perfect structure is an oval head and long tail. Abnormally shaped sperm may include a number of variations:

  • A very large round head. (In one study, if 14% or more of sperm had round enlarged heads, the chances for pregnancy fell to about 20%. Such an abnormality indicates early unraveling of genetic material.)
  • An extremely small pinpoint head.
  • A tapered head.
  • A crooked head.
  • Two heads.
  • A tail with kinks and curls.

Genetic Fragmentation

Sperm carry half the genetic material necessary to make a complete human being. (The egg holds the other half.) Genes are contained in the rod-like structures called chromosomes. The genes themselves are made up of chains of molecules called DNA, which carry the information that defines a human. Increasingly, experts are reporting that genetically fragile sperm may be very important factors in male infertility. Such sperm have fragmented DNA chains, which make them less capable of fertilization and may also contribute to low quality.


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