A new UK study of men's sperm counts, one of the largest of its kind, has revealed a drop in the average concentration from 87 million sperm per millilitre in 1989 to 62 million in 2002, a decrease of almost one third. The research was carried out at the Aberdeen fertility clinic in Scotland based on 16,000 sperm samples taken from 7,500 men. Whilst doctors at the clinic described the dramatic decrease as a cause for concern, they stressed that sperm concentrations above 20 million per millilitre are considered healthy. Aberdeen University's Siladitya Bhattacharya, who led the research, also stressed that as the study was carried out on men seeking fertility treatment, the results may not reveal a general trend. 'That is an inescapable fact. We weren't able to get a truly random sample. Nevertheless, the drop in sperm count must cause some concern, and needs to be explained,' said Dr Bhattacharya. The seemingly sudden fall in sperm count might also simply reflect an increased awareness of fertility treatment among men, he added. 'There has been an increase in men seeking treatment for male infertility, but whether this is due to a significant increase in this condition or because men are more aware of new techniques, we cannot say.' If the study does reflect a dramatic fall in male sperm counts in general, however, there is no shortage of theories as to what may be the cause. Smoking, excessive drinking, obesity, pesticides and even tight fitting trousers have all been proposed as potential culprits. The team from Aberdeen is now planning research into other aspects of the samples, including sperm mobility, to see if they can detect any further decline in quality that may point to a general fall in male fertility. Dr Alan Pacey, an andrologist at the British fertility society where the research was presented, had good news for men outside the UK, however. 'British men actually fare quite badly on the European stakes, and the region of Europe which is known to have the highest sperm count is Finland,' he said. At the same meeting of the British fertility society, another study revealed that the majority of couples undergoing in vitro fertilisation treatment were prepared to donate unused embryos for stem cell research. A survey of couples attending the Newcastle fertility centre revealed that 57 per cent were willing to donate supernumerary embryos to medical science. The chair of the British fertility society, Professor Alison Murdoch, said: 'When people understand this issue they tend to look on it favourably. Scientists should not be afraid of engaging the public on this issue.'