Campaign groups are backing a call for more research to be carried out into trends in infertility.
Jens Peter Ellekilde Bonde, professor of occupational medicine at Aarhus University Hospital in Denmark, and Jorn Olsen, professor of epidemiology at the University of California, said the ability to conceive will probably decline over time.
Their editorial in the British Medical Journal (BMJ) claims sexual behaviour, family size, social conditions, and the age at which people start to have children all affect birth rates.
The scientists conclude: "These cultural and social norms may mask more subtle biological changes in the population.
"More direct markers of fecundity are urgently needed, and the time has probably come to include fecundity in ongoing representative health surveys.
Dr Allan Pacey, senior lecturer in andrology at Sheffield University, agrees more research is needed.
He added that relatively little is known about genetic disorders contributing to infertility, saying: "It's right in that we need to explore it in much more detail."
And Susan Seenan, from the charity Infertility Network UK, said: "Infertility is an extremely distressing illness and has an effect on all aspects of your life.
"Any research which helps ensure that in the future couples are not faced with having to deal with the difficulties of not being able to conceive must be encouraged."