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Most men with fertility problems have one or all of these problems:

• Too few sperm (low sperm count)
• Abnormally shaped sperm
• Sperm that don't swim well.

A normal sperm sample should contain at least 40 million sperm or at least 20 million sperm per milliliter (ml for short). Half of these should be moving.¹

If you have fewer sperm than this, you have a low sperm count. This doesn't mean that you and your partner can't get pregnant, but it may take longer.

Doctors define borderline sperm quality as between 10 million and 20 million sperm per milliliter of semen, 30 percent to 50 percent mobile sperm and 4 percent to 14 percent of sperm with normal appearance.²

Doctors define very poor semen quality as less than 10 million sperm per milliliter of semen, under 30 percent mobile sperm and under 4 percent of sperm with normal appearance.²

Some men have a very low sperm count or no sperm at all.³ A low sperm count may be caused by:

• An imbalance of hormones
• Previous damage to the testicles
• An infection in the testicles
• Your genes: A low sperm count sometimes runs in families.

Sometimes doctors do not know why someone has a low sperm count.

Sperm may be abnormally shaped. They may have two heads or two tails, for example. This may stop them moving normally or fertilizing an egg. We don't know why this happens.

See More about sperm.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.