A Scottish study has found evidence to suggest
that men's sperm counts have fallen sharply in recent years.
Stopping smoking is a good first step for men trying to conceive
BBC News Online examines what men can do to boost their chances of having children.
What does this study say?
As part of this study, doctors tested 16,000 semen samples taken from 7,500 men who attended a fertility clinic between 1989 and 2002.
They found that the average sperm count of those men who had a "normal" sperm count had fallen by 30% during this time.
Why did their sperm counts fall?
Nobody knows for sure why men become less fertile or indeed infertile.
Studies have suggested a wide range of possible reasons.
Doctors usually point the finger at drug use, alcohol, smoking or obesity.
However, there is growing evidence that a man's environment may also be an important factor.
Pesticides, chemicals and radioactive material have all been linked to decreased fertility.
In 1986, Scotland was among the regions of the UK affected by the fallout from the Chernobyl disaster, after radioactive dust carried hundreds of miles by the
clouds came down when it rained.
How can men boost their fertility?
Men who want to have children are generally advised to adopt a healthier lifestyle.
Taking drugs, drinking alcohol and smoking are all out. Exercise is in.
Diet is also important. Seafood that may contain mercury should be avoided but a few cups of coffee each day may help to wake sperm up and boost a man's chances of becoming a father.
Men may also like to consider other changes to the way they live.
In 2000, doctors in France urged men trying to have children not to spend too long behind the wheel.
It followed a study which found that driving for hours on end can damage sperm.
The same may apply to those who cycle or work outside.
Italian researchers have found that exposure to traffic fumes can damage sperm.
Men who come in contact with pesticides or chemicals at work may want to consider a career change.
Studies have shown that men who are in regular contact with pesticides are less likely to conceive than other men.
They may also want to consider getting in touch with their emotions.
A British study carried out four years ago found men who bottled up their feelings were more likely to have fertility problems compared to other men.
Can men overcome fertility problems?
Simple lifestyle changes may be enough to help some men to have children.
However, others may need additional help. The first port of call should be your GP. They will be able to advise on the best course of action.
Medical drugs and surgical techniques can be used to treat some men with fertility problems. IVF is another possible solution.