Giulio Di Sturco was on a beach in Tuscany with his family when he got talking to a fellow holidaymaker. "Your daughter was born premature, wasn't she?" the man asked. As it turned out, the stranger was Professor Charles Christoph Roehr, president of the European Society for Paediatric Research and a world-leading neonatal intensivist and clinical scientist.

The doctor had recognised a dummy Giulio's daughter was sucking as a type designed for preterm babies. The photographer-filmmaker's first two months as a father had been spent in hospital watching over his then-tiny child in an incubator. The professor told Giulio all about his work at the pioneering Neonatal Intensive Care Unit (NICU) at Southmead Hospital in Bristol, UK – one of the few NICUs in the world specialising in helping babies born earlier than 24 weeks to survive.

"Foetal medicine is really new – 20 or 30 years old," Giulio says. "Premature babies are called 'miracle babies' because if they had been born in another time, they wouldn't have survived. Incubators have evolved so that now they can maintain temperature and humidity. Until five years ago, treatment was much more invasive. Charles tries to do as little as possible but to help the baby choose to survive." For example, the NICU encourages "skin to skin" contact between the baby and parents – carefully supervised by the intensive care nurses.

Yet he was also curious to witness first-hand what his daughter had experienced in the first minutes of her life – in France, where she was born, doctors resuscitate newborns behind closed doors, whereas in the UK parents are present. So he decided to spend a week in February 2022 shooting in Southmead Hospital. He has since returned several times, and this was only the start of a project that has become personally important to him.

A hospital presents many challenges for a filmmaker. Giulio originally considered using a hybrid camera but decided on the Canon EOS C70, which was compact enough to ensure he remained nimble and unobtrusive, shooting handheld, while offering high dynamic range and 4K shooting capabilities. "If you're shooting video, go for a video camera," Giulio remembers being advised. "That was a great suggestion. I removed myself from the idea of shooting stills. I was forced to think like a filmmaker.

"That said, it helped that I was a photographer first, rather than a video maker," he continues. "I'm more flexible, I need less kit to work with. In an environment like this, you can't really shoot in a team. A video maker would be used to having someone on audio, a second camera… I'm a one-man band."

Giulio's kitbag contained two lenses – the Canon RF 100mm F2.8L MACRO IS USM and the Canon RF 28-70mm F2L USM. "I'd say 80% of the time I used the latter," he says. "It was perfect when something was happening, like a birth or an emergency. I knew I could easily do a wide shot or a really close one. And then in the moments when everything was steady, I would use the macro lens to focus on the details. The combination of the two was perfect for the job."

The hardest part was getting permission from the families to film – understandably, since it's a lot to ask to record such a vulnerable time in their lives. "It's very sensitive," says Giulio. "Charles and the team knew the patients well and had an idea of who might be interested in being part of the film."

The fact that Giulio had gone through a similar experience himself was important. "I would speak with them, explain my story and why I was doing this."

Lighting also presented challenges. Babies receiving phototherapy for jaundice, for example, are placed in darkness under blue lights, resulting in a slightly sci-fi, futuristic atmosphere. "There were about 10 different lights in the room, all a different colour – it was a nightmare," says Giulio. "In the beginning I tried to use artificial lights, but then I realised the lights were part of the story – they tell you this is a hospital."

Interspersed with wider shots showing medical staff at work, Giulio used his RF 100mm F2.8L MACRO IS USM lens to direct viewers' eyes to the babies' tiny hands and feet, with everything else out of focus. "These shots remind you there is a baby there but it's not really visible. You don't have to see everything. You can listen to the sound and you can imagine what is happening."

The film is a work in progress, with more shoots planned at other NICUs. Whether it becomes a standalone documentary or a series, Giulio intends to show a "day in the life" on the Bristol ward through real-time experiences of medical staff, parents and babies, alongside interviews. He then hopes to do the same for other pioneering units around the world.

Although he is still haunted by the sounds of the NICU where his daughter started her life, making this film is a way "to give something back," he says, in publicising their work with this film once finished. "This is a world that I knew nothing about before. It takes incredible people to work in neonatal intensive care. And I wanted to pay tribute to them."