Dr John Kennedy has got used to the reaction from his male patients. It's a mixture of shock and disbelief. Few truly believe that the reason they and their partner can't conceive is down to them.
"There's still this idea out there that it's a female issue," the head doctor at the Dublin and Cork-based IVF clinic, Sims, says, "but that's absolutely not the case. Among my patients, I'm seeing the issue residing at least in part with the man 40 to 45pc of the time."
But despite such a high prevalence, the news is usually a bitter pill to swallow. "There are all sorts of feelings bound up with masculinity and this sense that men should be able to procreate," he says. "You can see it written in their faces. It's very difficult to accept."
It's thought that up to one in six Irish couples have difficulty conceiving so there's a large cohort of men out there who are either having to cope with the fact that they have fertility issues or, as is so often the case, not yet aware there's an underlying problem.
And the issue of male infertility has hit the headlines in recent weeks thanks to a ground-breaking study in Belgium which showed that boys born through a common type of IVF treatment are suffering from low sperm counts and may not be able to have children naturally.
It's a finding that does not surprise Dr Kennedy.
"There are root causes to sub-fertility," he says, "and they can be passed on to children."
He notes that the offspring of parents who had difficulty conceiving could face their own fertility challenges in adulthood, and that's certainly now seems to be the case for men.
Male fertility is one of the few remaining taboos. Men just don't want to talk openly about infertility - or, more accurately, 'sub-fertility', the less-than-normal capacity for reproduction.
Helen Browne knows about such a fear all too well. She is the founder of the National Infertility Support and Information Group and says men can find it difficult to accept that the issue lies with them.
"They are usually absolutely shocked," she says, "and it really upsets them, not just because it may mean that they may have difficulty becoming a father, but also about what they perceive it to say about their virility, their masculinity."
Some men, she argues, confuse virility - their sex drive - with fertility.
"Even the language used - 'to be man enough', for instance - is unhelpful." She recalls one man who had to put up with jokes from workmates about 'firing blanks'. "People don't realise how tough it can be for those going through IVF, for instance. It might be just banter, but it can be really hurtful."
It's talk that can make men share the burden alone. While women are far more likely to talk to friends about any sub-fertility issues they may have, she believes few men would be comfortable discussing such a private matter, even to close confidantes.
"Sometimes, before an evening meeting with the group, they'll have a drink to calm their nerves," she says. "It really helps when they get to meet and talk to other men who know exactly how they're feeling."
Dr Bart Kuczera of the Beacon Care Fertility clinic in Dublin is also familiar with the upset that men can feel about a diagnosis. "I remember having to tell a young guy who was super-fit, who did triathlons, and he just couldn't believe it," he says. "He thought he was doing everything right, and leading a very healthy lifestyle.
"But male fertility can be affected for all sorts of reasons, including being on the saddle of a bicycle too often or over-exercising. It's even thought that wearing tight underwear can be a factor. There's a list as long as your arm."
Dr Kuczera says lifestyle factors - such as diet, alcohol and caffeine intake - can play their part, as can exposure to certain toxins and excessive mobile phone use. Studies have also been conducted on how men who use laptops - on their laps - can have a reduced sperm count.
"But it's not an exact science," he says. "You can have people who drink a lot and have poor diets and have no problems at all, and others who seem to be doing everything right, but have an issue."
The key, he says, are the people in between - those who have an issue with their sperm and see positive results when they take positive changes in their lives.
Broadly speaking, male infertility can be attributed to four factors: low sperm count, poor sperm motility, malformed sperm and blocked sperm ducts.
Sometimes there are warning signs, such as undescended testicles - a common defect that men can be born with and can lead to infertility issues in adulthood, or orchitis - or the inflammation of the testicles/genital tract, which is caused by mumps.
One in six males is affected by varicocele, an enlarged vein in the scrotum which, if temperatures rise, can decrease the quantity and quality of sperm. And then there are genetic issues, such as cystic fibrosis and Klinefelter's Syndrome (chromosomal condition).
Dr Kennedy says that while men find it much harder to accept a diagnosis, the options open to them bear none of the invasiveness that many females have to endure. "It's a man's world in that regard," he says. "In many cases, the best course of action is a change of diet - minimising the amount of processed food eaten - and cutting back, or giving up, on the smoking."
Female patients, on the other hand, sometimes have to undergo a course of drug-therapy, much of it self-injected every day. "It was hard to see my wife having to go through that," says one Dublin-based thirty-something male, "especially when it was confirmed my sperm was of poor quality. They weren't definitely able to say that I was the sole reason why we couldn't conceive, but I feel as though I was.
"No matter how rational I try to be, I feel guilty every now and again that I can't give my wife the child we would both cherish so much. We've been down the IVF route and have tried other treatments too, but so far nothing's happened. It's tough, but we're not giving up. We both have a few years left. There's always the donor option, but we're not thinking of that for now."
The science around infertility is improving all the time and therapies like ICSI are proving to be enormously helpful in helping couples to conceive in those instances when the issue is with the man. ICSI - Intracytoplasmic Sperm Injection - requires just one sperm which is injected directly into the egg. The fertilised egg is then transferred to the uterus.
First used successfully in the US in 1995, it's a procedure that has helped transform the prospects of couples who would have been unable to have children in the past. It's become a popular choice in Ireland.
Tom, who is now in his early 40s, had been devastated to learn he had an abnormally low sperm count, but is now the father of a five-year-old girl who was born thanks to ICSI. "We'd been through the ringer," he says, "and I'd begun to think I'd never be a father. I come from a big family and always imagined that I would have at least two children too. I took it for granted. It was hard to learn that I was the reason we couldn't have children. I'm just very thankful that ICSI was available to us. It's changed our lives."
It's not the only medical advancement to help men with infertility problems. TESE - Testicular Sperm Extraction - is enabling men without sperm in the ejaculate to have a biological child. Essentially a testicular biopsy, it enables the retrieval of sperm from testicular tissue and can be either used on the day of the ICSI treatment, or frozen and stored for use at a later date. Doctors who work in the field in Ireland say data on male fertility remains thin on the ground. But it's widely accepted that infertility is on the rise.
Dr Kuczera says the fact that men are typically having children at a far older age today than they were in their parents' time is a definite factor in the rise. The average age to marry is a good indicator of changing trends. In 1976, Irish men married at 26. Today, it's 35.
"Sperm count declines as you get older," he says, "there's no doubt about that. Factor in the fact that their partners may be older too than they were in previous generations and it can be extra hard to conceive. I often see it in men in their 40s who are in a new relationship and want to start a family."
Such men may have had children in a previous relationship and are now having to come to terms with the fact that they may not be able to have any more, despite their best efforts.
"We have seen some remarkable results when there's been a change in lifestyle," Dr John Kennedy says, "but there are no guarantees." He says every couple who has infertility issues are likely to find the experience to be emotionally taxing.
It is not uncommon for some people to have multiple rounds of IVF - and with no certainty that conception will happen. Helen Browne went through seven rounds, but to no avail. She is philosophical about the experience today, pointing out that she and her husband did everything they could to conceive. There are no regrets, especially now that she can draw on her own experience when it comes to helping others.
She established a support group almost 20 years ago. Information was thin on the ground then, and she found that people were phoning with questions about IVF and other treatments. Helen says there still a huge lack of awareness out there among the wider population.
"It's commonly assumed that infertility is almost always down to the women, but it can and does affect both partners and there's a high incidence of the issue in men exclusively."
And, yet, it's almost always who female partner that seeks treatment when conception fails to happen. Helen says virtually all calls that come through to the helpline are from women - and there calls from new people come every day.
"I hate to think that there might be men out there suffering in silence," she says.
"I always say it takes two people to have a child and no one partner should feel guilty."
It's a sentiment shared by Dr Kuczera.
"You wouldn't feel guilty if you got cancer, so why should you feel guilty if you have issues with fertility? In my experience, the women are very supportive of their men. There's no blame being attributed. Both people are in it together. That support is very important. It can be a stressful time, so you need the support of your partner and those people who are close to you."
But sub-fertility can cause relationship woes. Tom - quoted above - says he and his wife found the going tough when every passing year presented new failure.
"We found that we'd be snapping at each other a lot," he says. "And the thoughts of having a family consumed us. Sometimes, it was hard to be out and about and see fathers with young children. I'd wonder why that wasn't me, but I'm much more accepting now. There are obstacles and challenges in everyone's life - this is mine."
But while fertility problems and associated treatments like IVF can be emotionally taxing, what's often not talked about is the high cost. A round of IVF starts at €5,000 and can rise to €10,000 if donor eggs are required. It's not uncommon for couples to spend €50,000 on multiple rounds.
And yet, despite the high cost, IVF has become a commonplace feature of Irish life. Sims in Dublin carries out around 1,400 IVF and egg-donation cycles every year and that's just one of 28 clinics offering fertility services in the Republic, according to the whatclinic.com website.
An indication of how popular IVF has become can be gleaned from the high number of twins born each year. More than 1,200 mothers in Ireland have delivered twins every year since 2009. Before 2000, the figure hadn't topped 200. There's a 10 to 20pc chance of twins for every successful IVF.
"The treatments are proving to be successful for a lot of people," Dr John Kennedy says, "and the more known early the better." The earlier a couple presents with a problem the better, from a fertility clinic point of view.
For couples under 35, inability to conceive after 12 months of contraception-free intercourse officially counts as sub-fertility, while according to the American Society for Reproductive Medicine, it is advisable for women over 35 to see their doctor if they can't conceive after six months.
While Dr Kennedy may have got used to the anguish many men feel when told a fertility issue lies with them, the flip-side is the joy among those for whom treatment is a success.
"It means so much to them," he says. "In many cases, they could have been through years of not knowing whether or not they would ever have a child."
Rewind 12 months, to October 2015, and Paul Bradley was hearing the news that left him reeling. The results of a special test had come through from the fertility clinic he and his wife were attending, and there was little doubt about it: the reason Paul and his 30-year-old wife Kristel could not conceive was down to him, not her, as both had originally assumed.