Is male infertility on the increase?

Infertility affects one in six couples in the United Kingdom. Male infertility is now the single most common cause. Compared with animals, human conception is, at best, inefficient. From one act of coitus a man can eject some 500 million sperm, yet a mere hundred survivors will reach the ovum. As a result anything less than 20 million sperm per ml of ejaculate significantly reduces the chance ofconception. This is why there is growing concern about the apparent trend in the Western world over the past two decades which shows a decline in sperm counts. The 'quality' of human semen is also very poor compared to other mammalian species. A large number of human sperm have morphological abnormalities and, according to the WHO classification, a human semen sample is to be considered normal even if 50% of the sperm are not moving progressively (ie exhibiting space-gaining forward movement).