Shortly after my daughter was born, I found myself kneeling on the floor of our house in Nottingham, carefully cutting her out of a babygrow with a pair of scissors. There was no emergency – I was simply so overwhelmed at being left alone to look after her, and she looked so fragile that I didn’t want to hurt her by bending her delicate little arms. So I resorted to scissors.

I am sure most new fathers feel helpless, and even after nine months’ preparation, terrified of doing the wrong thing. But I didn’t even have the luxury of those nine months of pregnancy to get ready – I had just three hours’ notice. At 11.45pm on 11 May 2015, I was 29, carefree and child-free. By 12 May 2015 at 3am, I was a dad.

Had we known, we certainly wouldn't have gone ziplining the weekend before Lyndsay gave birth

It began with my girlfriend’s “appendicitis”, as diagnosed by the 999 operator. Except it wasn’t: she was in labour. Until then, Lyndsay, whom I had been with for three years, had no symptoms of pregnancy: she had been taking the pill and had even been losing weight. Neither of us even remotely considered she might be pregnant.

That day, I hadn’t heard from Lyndsay since lunchtime, so I was blissfully unaware until her mother called me at 11.50pm. I knew something was seriously wrong, because she refused to say anything until I was sitting down. When she said Lyndsay was in labour and I was going to be a father, I couldn’t speak. The baby was coming, imminently.

When I put the phone down I stood there, stunned, my mind in overdrive. I wasn’t ready to accept the responsibility; everything was happening in the wrong order.

I had always said that I didn’t want children, but if ever I chose to, it would be after marriage. The very idea of fatherhood made me shiver in fear; I had never even held a baby. I had to get to that hospital, but I couldn’t think straight, so I phoned my best friend. She was equally confused and surprised, but stayed with me on the phone for the entire journey. She told me to think about Lyndsay, who would be terrified, and to keep her posted. Just sharing the news helped calm me down.

When I made it to the hospital, Lyndsay’s mother was waiting for me. As she led me down the corridor to the maternity ward I felt as if I was walking the Green Mile. At the same time, I was desperate to get to her.

‘As soon as the front door closed and I placed Bella into her moses basket, everything felt calmer’: Adam, Lyndsay and Bella in their garden. Photograph: Fabio de Paolo/The Guardian

As I entered the delivery room, Lyndsay was still insisting to the midwife that she wasn’t pregnant and, in between words of denial and inhaling gas, rolled around in pain on the bed. When she spotted me she burst into tears and blurted out how sorry she was – she knew I didn’t want children. I did all I could to reassure her it was going to be OK, but the truth wasI didn’t have a clue what was going to happen.

The midwife showed us our baby on a monitor, but it was too late to determine the sex or health; Lyndsay just had to go for it. She was already 8cm dilated and told that she couldn’t have an epidural. I held her hand tightly as she cried out.

It was approaching 3am when our daughter was born, and I was the first to hold her. She was wrapped in a towel and had an angry, confused cry and yet, as I took her from the midwife, I felt nothing but unconditional love. I had convinced myself fatherhood would be my own personal version of hell, but at that moment I understood how wrong I’d been.

I didn’t know what I was doing. I was sleep-deprived, scared and ​​clueless

It wasn’t until later that morning, alone with our daughter for the first time, that it dawned on us: she had no name. We chose Bella – the first I suggested. We discussed how Lyndsay andBella would move in with me and that I would be there, despite the challenges.But that was the easy part. Apart from a 10-minute conversation I had with a nurse, who told me to “support the head and you can’t go wrong”, I didn’t know what I was doing. I was sleep-deprived, scared and clueless.

Then social services unexpectedly turned up to talk to Lyndsay in hospital. They explained they had to look into all cases of “concealed” births, just in case of familial abuse. Lyndsay described how she had recently been feeling extra tired but had assumed that it was down to a new job, not a baby. (The midwife explained that Bella had been hiding in her back, hence no bump.) I was also visited at home to ensure that it was a suitable environment to bring up a child.

We reflected on the places we’d been and the mad things we had done while Lyndsay was pregnant. We certainly wouldn’t have gone ziplining the weekend before Lyndsay gave birth, had we known.

Four days later, Bella and Lyndsay came home. By then I wasmentally much more prepared. As soon as the front door closed and I placed Bella into her moses basket, everything felt calmer. My perspective on the world had totally changed in the space of those three hours, between finding out she was on her way and her birth. I had grown up overnight.

• 3 Hour Dad is now available as an ebook from Amazon or iBooks, and £1 from each sale goes to anti-bullying charity Kidscape.

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