Infertility a huge shame men carry with great sadness
There are three main criteria by which male sperm is assessed: volume, mobility and shape. When Russell Davis visited a Harley Street clinic for a test after he and his wife were struggling to conceive, he failed on every count.
"It was disastrous," says the 42-year-old. "The doctor even asked me if I had ever been exposed to dangerous radiation because it was so bad.
"I had no family history of infertility .. It was such a kick in the teeth. I felt . it was my fault and I couldn't do what every man should."
On such simple laboratory results, so much of masculinity depends. Perhaps this is why male infertility is rarely broached, even though it is responsible for 30% of infertility problems. This was a fact noticeable by its absence in the maelstrom prompted by Professor Geeta Nargund's comments last week, when she said that unless women started trying for a baby before they are 30, Britain faced a "fertility time bomb".
"It's hard to define the scale of male fertility," confirms Professor Allan Pacey, a leading male fertility specialist at the University of Sheffield.
"Men can be really devastated by an infertility diagnosis and many don't cope with it very well."
There is no "cure". Couples can either undergo Inter-cytoplasmic sperm injection (ICSI) - where a single sperm is chosen to inject in the egg - or seek a sperm donor.
Paul, 41, and his wife opted for the latter.
"You grow up in a society where the very essence of being a man is potency and fertility, so if you don't have that it becomes this huge shame that you carry. It really affects your sense of self. It takes a lot of time to admit to yourself you are infertile ."
He and his wife chose a donor together, although Paul says many men find the process too difficult. Two years ago his wife gave birth to twins.
"You have to allow yourself to be sad and mourn the children you couldn't have," he says. "That can be quite heart-breaking, but it stopped when she gave birth. Children are such mimics; they stand like me and laugh like me."
Darren McCluskey, 43, has been trying - and failing - to conceive through ICSI for more than a decade now.
"There are times that creep up on you. You see a father with children in the supermarket or playing football and it grabs you at an unexpected moment."