Sperm morphology (normal forms)

The WHO lower reference limit is 4 %; the fertility team interprets the whole picture.

The percentage of sperm with a normal shape under strict criteria. Even in fertile men most sperm look abnormal under these criteria, which is why the reference limit is so low. Semen analysis is interpreted as a whole by the fertility team, using WHO reference limits that describe the lower 5 percent of men who fathered a child within a year. A single sample below a limit is repeated after two to three months, because production varies a great deal and takes about ten weeks.

Part of every semen analysis, requested in fertility clinics and after vasectomy (where the aim is no sperm at all).

• Nothing in particular; a high value is unusual

• Heat, illness, smoking and toxins
• Varicocele
• Some inherited patterns

• Production varies a great deal between samples from the same man
• Abstinence of less than two or more than seven days changes the result
• A sample that reaches the lab late reads poorly

Two to seven days of abstinence, collected into the lab pot, delivered within an hour and kept at body temperature.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.