Like women, men have been found to suffer from a ticking biological clock, that affects fertility from their mid-30s.
The new research indicates that delaying fatherhood can substantially increase the risk of fertility problems, with the chance of falling pregnant decreasing once the man is over 35.
The French study followed 12,200 couples that were having fertility treatment, at a Paris centre over a five-year period.
All the women were treated with artificial insemination, which is often when the woman is not suffering from fertility problems.
The men's sperm was examined by the researchers, and tested for shape, size, quantity and ability to swim.
The number of births, pregnancy and births were then recorded.
Although it has long been known that woman's age was significant, the results also showed that men's age affected chances of conception.
Women over 35 were shown to a higher rate of miscarriage and lower rate of pregnancy, but the miscarriage rate was also affected by the age of the man.
If the man was over 35, then the risk of miscarriage was higher than if the man was younger, and couples were a third less likely to conceive. When the man was over 40, then the chances again became lower.
Overall, when the man was between 30 and 35 the successful pregnancy rate was 13.6 per cent. This fell to 9.3 per cent when the man was older than 45.
The decreased rates were attributed to a number of factors, including that the sperm's DNA may decay with age.
Dr Stephanie Belloc, who presented the work to the European Society of Human Reproduction and Embryology conference commented, 'This research has important implications for couples wanting to start a family.'