When the birth of a baby is registered in Britain, the ONS takes fertility details for the mother of the child. This gives researchers all sorts of information about how motherhood changes the lives of women - whether or not it makes them happier, physically healthier or more likely to earn a higher wage.
But no such records are taken for men. Because of this, no one even knows exactly how many fathers there are in this country, never mind how becoming a dad changes a man. Even less is known about what it's like not to be a dad when you want to have a family. This is a taboo subject that most men still don't know how to discuss.
As a childless man of 64 who has always wanted children, here's the truth: it's an isolating and at times crushing experience. There's a unique grief that comes with unintentional childlessness, but men like me are assumed to be happy, and constantly told that we're "free". You wouldn't tell a woman the same. People look at you like you're strange when you reveal that you've always dreamed of being a dad.
Before you assume that I'm some sort of desperate loner, you should know that I've had my opportunities to be a father. I got married in my early 20s, to a woman who wanted children, but things didn't work out between us and I became a divorcee before I turned 30. I then got into a relationship with another woman who wanted children with me, but we weren't meant to be. It was only in my late 30s that I met my wife, Maryan, who I've been happily married to for the last 20 years.
My own dad was middle-of-the-road, not good but not especially bad, either. By the time my 20s were over, I really wanted to give the sort of close parental bond I'd always longed for to a child. My 30s became an intensely broody time - I was constantly thinking about how badly I wanted a family, and my envy for my friends with children grew and grew.
Because we men don't tend to put a word to the broodiness we have, those feelings were confusing and distressing. In other areas of life too men are conditioned not to express their feelings. Keeping your emotions bottled up takes a toll on you psychologically. It should be no surprise that, on average, childless men are angrier and more depressed.
As all my friends were starting to have their first children, I developed an intense feeling of being "behind" in some way. There's still social status attached to fatherhood, too, so I began to feel lesser than my peers. It didn't help that everyone my age was suddenly unable to come to the pub with me after work or spend time with me at the weekend.
I remember clearly the moment that I realised I would never be a dad: Maryan and I had just bought a house in Manchester, shortly before we got married, and I was papering the walls of one of the bedrooms, where I'd thought one of our children might sleep one day. I felt absolutely miserable - the wallpaper kept falling down, and one of my best friends had just become a dad, which felt to me like a reminder that I had fallen behind in life.
I called Maryan, who was in London for work, and told her how I was feeling. She said, "If you want children, you need to accept that that isn't going to happen with me." Maryan had desperately wanted to be a parent in her 30s too, but into her 40s her desire for children began to wane. For one, she felt that as an older couple with less energy, we might not be able to handle the work that having a child with a life-limiting disability could require. The chances of this rise after a woman reaches her mid-40s, when realistically we would have had our first child together.
You might ask why I didn't leave Maryan and try to find a younger woman, if having children was so important to me. Men are told that this is always an option if you haven't had children by your mid-30s - there's no "biological clock" that can run out for us. (That's wishful thinking anyway: the chance that you can have a biological child declines from your mid-30s onwards).
First and foremost, I just wasn't willing to end a relationship with the person I loved for the prospect of having children with someone else. But by the time you're nearing 40, most younger women won't be interested in you. In reality, you won't be interested in them as life partners, either.
By then I had befriended lots of childless 20-somethings, and I didn't want to keep up with younger people and their lifestyle of partying, drinking and doing drugs anymore. I was ready to settle down and the prospect of a relationship with someone 10 years younger than me didn't appeal.
Adoption is not easy either. Maryan and I did consider it, but we would likely have been adopting an older child whose background may have been very difficult. If we knew we couldn't properly care for a child with a disability, how could we hope to be good parents to a child who could well be traumatised, either?
Over time I accustomed myself to the idea that I would never be a dad, but I still had a love for children. I find them fascinating. I enjoy spending time with my friends' children, even with their teenagers, and it makes me happy to hear kids playing on the street or in my neighbour's garden. For women, that's expected, but men in my position who still love children are sometimes treated as if we might not have good intentions.
That's another layer of isolation as I age, and so is the fact that now, in my 60s, some of my friends are becoming grandfathers. For a brief few years they'd had the time to come out for lunch on the weekends, and while I'm over the moon for them and their families, it's hard to see that companionship slowly disappear again.
That's not to say I don't have a good life. As well as having a brilliant partner, my own experiences with childlessness have led me to a new career in researching the impacts of infertility and childlessness on men.
Having been a trainee technician and then a technical photographer for the University of Manchester since I left school at 16, with few qualifications, I decided to re-train as a counsellor in 2003, when I was 43. At the end of my masters' course in counselling, in 2007, I had to write a dissertation related to mental health, and chose the topic of male infertility, because not much research had been done into its effects on men.
That then led me to a funded PhD at Keele University, where I looked at how being childless affects men in their old age, when they might not have immediate family to care for them. Around one in five women in Britain doesn't have children, but the figure for men is thought to stand at around one in four, so this is an issue that affects us disproportionately.
The experiences that other men have with childlessness, documented in my own research and the work of others, has shown me that I was far from alone in the broody feelings I had in my 30s - in fact, one study I led showed that men are just as likely to feel broody as women.
Because of the stigma around it, being involuntarily childless affects us men all the more strongly: four in 10 childless men report being depressed, compared with three in 10 childless women, and twice the amount of men I interviewed said that they felt a strong sense of isolation.
While I still wish I had been a father, I'm glad to have found a life of meaning in helping to explain men's experiences with childlessness. I see it as a sort of parenthood, passing on what I've learnt throughout my life about this little-discussed topic to future generations, so that one day there will be more understanding of the issue. I only hope that one day the stigma around male childlessness and infertility will be less stifling and we'll be able to talk about the issue more freely.