Male infertility can be caused by a variety of factors, including lifestyle choices such as smoking or drug and alcohol use. Yet infertility is often a side effect of conditions beyond the man's control - like carrying the gene for cystic fibrosis.
Craig Smith's sister died from cystic fibrosis - a genetic, life-threatening disorder that damages the lungs and digestive system. Later in life, Smith discovered that he carried the gene for the disease.
After trying for a baby for more than a year, Smith took a sperm test. He was subsequently informed that his semen contained zero sperm.
Appearing on The AM Show on Monday as part of its Big Picture series, Smith revealed the emotional toll that infertility has taken on his life.
"As a gene carrier, there is the potential to be born with a natural vasectomy," he shared.
"As blokes, we don't talk about this… the guilt a bloke carries, it should be our job - we should be able to have kids.
"It's really emotional."
The AM Show co-host Mark Richardson - who revealed in 2017 that he and his partner had initially struggled to conceive as his "swimmers were a little slow" - added his two cents.
"You feel there is something wrong with you," he said.
"A basic human function and you can't provide it."
Smith is still able to produce sperm - however, like the large majority of men with cystic fibrosis, the sperm is unable to travel from the testicles to the ejaculatory duct.
According to the Men's Clinic at the University of California, Los Angeles (UCLA), the vas deferens - the tube in the male reproductive system that transports sperm to the ejaculatory ducts - is missing or blocked in men with cystic fibrosis. If a man has no vas deferens, the sperm remains trapped in the epididymis, which carries and stores sperm cells.
Non-profit academic medical centre Mayo Clinic notes that tube defects can be caused by a variety of reasons. Blockages may be due to inadvertent injury from surgery, prior infections, trauma or abnormal development, such as with cystic fibrosis or similar inherited conditions.
"You're born with a natural vasectomy, but you still make sperm," Smith explained.
According to Cystic Fibrosis New Zealand, sperm is normal in 90 percent of men with the disorder, so conception is still possible through in vitro fertilization (IVF) and a procedure called intracytoplasmic sperm injection (ICSI). During this process, a tiny needle is used to extract sperm directly from the testicles, which is injected into an egg.
However, these procedures are not always successful.
"At the IVF clinic when you're going through it - we had eight five-day blastocysts, the good ones - and they all failed. When you go there, you have the councillors saying, 'be prepared that this [might] fail'," he said.
Smith also revealed that the deterioration of his first marriage was partly caused by their inability to get pregnant, as he struggled to come to terms with his infertility.
He is urging men to be more open about their struggles and continue the conversation around male infertility.
"Us blokes, we need to start talking about it," he said. "Now that I've talked about it, it's starting to heal - but it's taken a long time."
Although Smith has been unable to have a child of his own, he is a stepfather to his wife's 18-year-old son.
"I have kids involved in my life but it's still never the same. There's still this hole in me, I suppose... There will always be that, and it's bloody tough," he shared.
"It's a big journey and we just need to get out and talk about it. Every time I tell my story, I feel a bit better."
In a third of cases of male infertility, the underlying cause is unknown. In order to get a partner pregnant, the man needs to be able to produce a sufficient quantity of healthy, functional sperm that is able to move. It also needs to be present in the semen.
Aside from defects in the tubes that transport sperm, male infertility can also be caused by hormone imbalances, environmental causes, undescended testicles, tumours, infections, certain medications, or problems with sexual intercourse or ejaculation.
Although there are treatment options available, roughly 75 percent of cases cannot be corrected.