INFERTILITY will become more common in future generations, with more couples needing help to have a baby, experts warned yesterday.
It is already estimated that fertility problems affect about 15 per cent of would-be parents in affluent countries.
But researchers, writing in the British Medical Journal, have predicted that such difficulties are set to become much more prevalent in the coming years, with a combination of medical, environmental and social factors affecting fertility.
They called for more research to be carried out now to combat infertility.
Jens Bonde, from Aarhus University Hospital in Denmark, and Jrn Olson, from the University of California, said measuring infertility was not simple.
The experts said that because fertility was linked to social, behavioural and biological factors, it was hard to determine to what extent each was responsible for the problem.
Environmental factors, such as exposure to certain chemicals, may also affect fertility.
One theory suggests that environmental chemicals may interfere with hormones.
But the experts said genetics were also likely to play a part. "Fecundity (fertility] is expected to decline over time, even if no evident causative environmental exposures are present," they said. "This is because fecundity probably has a strong genetic component."
Such a theory means that couples with poor fertility who conceive using techniques such as IVF could then pass the same problem to their offspring.
"With the advent of assisted conception, 'subfertile' couples may have as many children as fertile couples, so genetic factors linked to infertility will become more prevalent in the generations to come," the experts predicted.
They said that the best way to counteract infertility was to deal with avoidable causes.
One study found that men with the sexually transmitted disease chlamydia had a three-fold higher level of DNA damage in their sperm than men without the infection.
It is also known that obesity is linked to fertility problems.
The experts concluded: "There are good grounds for promoting further research and for trying to make up for the many years during which research into infertility has been neglected."
Prof Siladitya Bhattacharya, head of the department of obstetrics and gynaecology at Aberdeen University, agreed several factors were likely to have an impact.
"As well as the medical factors, the social effects of women deferring childbirth will also affect fertility rates," he said. "Most expect to stop using contraception and become pregnant immediately, but it rarely works like that."
Prof Bhattacharya said Scotland and other countries battling declining populations faced extra challenges. "It is right that we should focus resources and research on this issue now because of the likely impact it will have in the future," he said.
Susan Seenan, of Infertility Network UK, said: "Infertility is an extremely distressing illness.
Any research which helps must be encouraged."