Older men are up to five times more likely to father children with birth defects, according to some studies.
Experts claim that after 35, the risk of chromosomal abnormalities such as Down's Syndrome increases in proportion with the father's age.
Father and daughter
Men are being warned not to have children too late in life
Children born to older fathers also appear to run an increased risk of autism, say researchers.
A study of more than 70,000 births using records in Denmark of mothers under 29 and men of any age found the risk of a number of syndromes went up with increasing paternal age.
A 45-year old man is almost three times more likely to father a Down's child than a man under 30, while for men over 50 the risk is almost fivefold.
The risk of having a child with a cleft lip doubles for a man aged over 50.
Down's Syndrome cases soar as women delay a family
The results show the risk of some congenital conditions starts to rise when the father is between 35 and 40.
French research suggested over-40s are three times more likely than younger men to father a baby with Down's.
Miscarriages and stillbirths increase with advancing age of the father, which suggests rates of genetic damage could be even higher but many pregnancies do not progress.
Studies have shown that men's fertility declines with age - in much the same way as women have less chance of conceiving as they get older.
Older men's sperm is also less likely to undergo a self-destruct mechanism called apoptosis, which is meant to get rid of damaged cells.
It might not be only chronological age which affects sperm quality, but also the environmental damage that comes with age.
The organs involved in sperm production can be affected by smoking, chemicals, sunlight and lifestyle.