Few young men worry about their fertility. Most of them want to delay fatherhood as long as possible, and many take an "it'll be alright on the night" approach to their chances of success.
But such confidence increasingly looks misplaced. More and more research is finding that, in many cases, problems with sperm are responsible for a couple's inability to conceive.
That turns accepted wisdom on its head. It used to be thought that, because men produce billions of sperm for every female egg, infertility was far more likely to be a female problem.
Here's what the latest science is saying, and what you can do to protect and enhance your fertility - even if you're not planning on becoming a father for a few years yet.
Men are often the cause of infertility
Every year around 50,000 couples are told they're unlikely to conceive naturally and may need fertility treatment. Of those, around one-third have unexplained infertility, which until recently meant no obvious problem could be detected but the couple were failing to conceive anyway.
Now new research suggests that in most cases of unexplained infertility, problems with sperm are the cause.
The study, by Professor Sheena Lewis of Queen's University Belfast, examined the sperm of 239 couples with unexplained infertility, and found that 80% had high sperm damage - breaks and tears in the sperm's DNA.
Not only does that damage make it less likely that couples will conceive, it also makes it more likely that women who do conceive will miscarry.
"For almost one third of couples, until now, there has been no obvious cause for infertility and these couples are given the diagnosis of 'unexplained fertility'," says Professor Lewis.
"In our study, we have now had a breakthrough which explains the cause of infertility for many of those couples."
Why are men becoming less fertile?
So why are men suddenly becoming the focus of fertility research? Why is sperm under the microscope?
According to experts, male fertility is declining for the same reason female fertility is declining. We are leaving it much longer - often into our late 30s and beyond - to try to start families.
"It is now 50/50 with male/female infertility, whereas 10 years ago it was more a female factor," says Zita West, founder of the Zita West fertility clinic. "Age does have an important impact on male fertility, and sperm does decline with age.
"The older you are, the more likely you are to have free radical damage. Free radicals are a by-product of our metabolism and in lower levels are a good thing, but at high levels can be damaging to sperm."
Adding to the problem of age is the problem of our lifestyles. By trying for babies later, we're giving our self-destructive habits even more time to adversely affect our fertility.
"Lifestyle factors that increase free radicals such as alcohol, cigarettes, processed foods, and drugs can all damage sperm," says West.
How can men boost their fertility?
Given the connection between age and sperm damage, the most important thing many men can do to preserve their fertility is to not leave trying for a baby too late.
Experts now agree that a decline in male fertility starts at around the age of 35, and studies show that while 8% of men under 25 take more than a year to conceive, the figure jumps to 15% when men hit 35.
For men over 45 it takes, on average, five times longer to conceive than for men under 25.
After that, says Zita West, the best advice is to cut back on the lifestyle factors that undermine sperm. Eat a balanced and nutritious diet avoiding excess fats and sugars.
"The concentration of sperm among male smokers has been found to be 17% lower than non-smokers," she says, so quitting smoking is probably the first thing you should do to improve your fertility, along with avoiding illegal drugs.
In men, excessive drinking also reduces sperm count and motility. "One study showed a lower pregnancy rate for couples where the man drank more than 10 units per week," says West. "Avoid alcoholic binges and do not exceed more than three or four units on any one day."
If you're actively trying to conceive, you should exercise, but avoid overdoing it, and cyclists should avoid prolonged periods in the saddle. If you're hoping to conceive soon it's also worth avoiding tight underwear, steamy saunas and piping hot baths. Cool testes produce better sperm.
According to the famous Mayo Clinic in America, men should also maintain a healthy weight - there is some evidence that obesity undermines sperm quality - and manage stress.
In other words, there's no shortcut to healthy sperm. As the new research shows, men are as likely to be the cause of infertility as women, and men's fertility drops with age just as women's does. Improving your chances of easy conception is down to the usual suspects of health. Do the right things for the rest of your body, and you give your sperm the best start in life, too.