THEY are 15 centimetres long with heads as big as 10¢ pieces - and they've never been seen on this scale.

Fertility specialists at IVF Australia have developed technology which magnifies human sperm by 7300 times its normal size - about 18 times larger than they have ever been seen.

The digital imagery gives scientists their clearest picture yet of which sperm are most capable of fertilisation.

The technique is being used to help men whose partners have experienced repeated infertility or miscarriages due to DNA damage to sperm or significant morphology problems, such as sperm with oddly shaped or multiple heads.