Research suggests that older men face an increasing risk of fathering children with abnormalities, just like women. David Labanyireports
Men have long held a rather relaxed attitude when it comes to what age they should start a family, or indeed a second family.
An image of lifelong fertility is due in part to famous elder fathers such as Charlie Chaplin and Pablo Picasso who fathered children late into their 60s.
However, recent research increasingly suggests that as men enter their 40s and 50s they too, just like women, may face an increasing risk of fathering children with abnormalities.
The studies show that despite not having a fixed "andropause", rates of some birth defects such as achondroplasia (short stature) and autism appear to be higher among children with older fathers.
Prof Sheena Lewis, a consultant in reproductive medicine at Queen's University Belfast, says one of the causes of these problems is that as men get older their sperm DNA becomes more fragmented.
"If the sperm DNA is damaged it has a number of negative effects.
"It can affect fertilisation, it can affect embryo quality, implantation rates and it can also affect the health of the next generation.
"There is no one cut-off point for men similar to the menopause but we know if we take cohorts of each 10 years there is more damage as time goes on."
She says men are generally unaware that they may face these difficulties. Older men attending the fertility centre in Belfast with younger partners are often surprised that the issue could be with them, Lewis says.
"The message that has got through to the public is that women's fertility has a shelf-life but men's does not," she says.
While women are born with a lifetime supply of eggs, men constantly produce new sperm as the stem cells in the testes constantly divide. It is estimated that by the time a man is 50 years old the cells that create his sperm have split and replicated up to 800 times, with each round creating the possibility of an error.
Lewis also says men need to be aware of the impact of modern lifestyle and environmental factors on fertility.
For example, few couples realise that the impact of the father smoking is even worse than the mother smoking, Lewis says.
"Fathers who smoke increase oxidative stress and cause DNA damage in their sperm. You can't repair damage you get in sperm DNA."
Award-winning research by Lewis's team in Belfast has also found that Viagra can affect fertility by causing the sperm to travel too fast, diminishing its effectiveness.
When her team examined the impact of cannabis they found the opposite effect, the sperm function is slowed, also leading to a reduction in fertility.
"I'm not too sure men are aware that recreational drug use can affect fertility in that way or that issues such as alcohol use can affect fertility."
In a book published in the US, The Male Biological Clock, Dr Harry Fisch, an expert in male reproductive medicine, suggests men also have a reproductive bell-curve similar to that of women which begins at puberty, peaks and then starts to decline from his mid-30s, although less dramatically and completely than with the menopause.
Fisch contends that most fertility treatments ignore the man's reproductive potential and concentrate instead on the woman.
He says the use of more complicated treatments such as IVF could be reduced if the role of male fertility was better understood.
Prof Andrew Green, director of the National Centre for Medical Genetics at Our Lady's Hospital Crumlin in Dublin, says it is well known that women in their late 30s and older have a higher chance of having a baby with chromosome problems. However, he says there is some evidence that new gene alterations in the child are more associated with older fathers.
"There is a genetic condition called achondroplasia which causes a person to have small stature and the average age of fathers of people with achondroplasia is actually higher than you would expect.
"And that is probably because this specific gene alteration occurs in an older sperm," he says.
"There has also been one study that suggests that a small number of children who have autism [ that] it might be associated with the age of the fathers, although that hasn't been confirmed."
In this study researchers analysed a large Israeli army database to examine if there was a correlation between the age of the father and the incidence of autism and related disorders.
They found that children of men over 40 were 5.75 times more likely to have an autism disorder than those who had fathers under 30.
Another Israeli study which examined the occurrence of schizophrenia in children suggested the risk is almost double in fathers in their late 40s.
He admits the area is not particularly well researched and that different researchers use different ages as a cut-off point, for some studies it is men over 40, for others men over 50.
Ted McDermott, a consultant urologist at Tallaght and St James's hospitals in Dublin, says many of these issues were discussed at a recent meeting of the American Society of Male Infertility.
He says the feeling among medical professionals at the meeting was that "older males and people going into infertility programmes such as IVF should be advised that there is an increased risk of abnormalities and certainly the quality of the sperm reduces as well".
McDermott says the age at which problems become more prevalent has yet to be clarified but he suggests it is mainly males over 50.
"There was a lot of disagreement at the meeting about what to say to people because the statistics aren't out there to show how big the problem is, but the overall feeling is that there is a problem," McDermott says.
He says the area is now receiving more research attention particularly as the number of males having families in second and third relationships, with the aid of IVF, is increasing quite dramatically.