Guess who's having a baby: Joe Penhall's new play, Birthday, tackles childbirth – with a twist

Joe Penhall is proud to have been present in the delivery room for the births of both of his sons – William, now three years old, and Ned, one. "I was right there. In the pitstop," he says, shaking his head violently. "And I was, to my great shame, thinking, 'Yeah, this is good, this is good…'" Good material for a play? "Well, no. Because it was quite scary and horrible, but I did think, 'God, why hasn't anyone done this?' It has all the things that drama eats up. Danger, jeopardy, high emotion, complex psychology, conflict and suspense. The suspense is agonising. Terrible! Hours of not knowing what's going to happen."

The playwright, 44, stopped short of taking notes between contractions but by the time he emerged from the labour ward, 17 hours later, he knew that he had to write about the experience. "And I knew the time to write it was while it was still fresh out of the oven." So he went home, had a couple of stiff brandies and started writing while his wife's stitches healed in hospital. A week later, by the time baby Ned was settled into his new cot, Penhall had given birth himself – to a new play.

Birthday is a bold, bloody comedy set around a hospital bed in the excruciating hours before birth. Breaking waters, ambulance dashes and the screams and smiles of labour have long been a mainstay of television drama but Penhall set out to subvert that. "As a rule of thumb, when people start writing about their own parenthoods, that's when it starts to get boring. There's something somnolent about hearing about other people's children and childbirth," he says. "There has to be a way of doing it that penetrates people's sleepy assumptions."

And what better way to jolt Royal Court audiences out of their comfy leather seats than by showing them the whole messy process on stage – every last groan, gasp of gas and groping internal exam. Oh, and by making the character who is giving birth a man. Past master of the theatrical twist, in this, his 10th play, Penhall is pulling off the ultimate eye-catching switcheroo. It is the male lead, Ed, who sports the bump and backless gown and spends the play being prodded and probed while his wife, Lisa, sponges his forehead and scolds the nurses. Stephen Mangan and Lisa Dillon play the modern couple who have decided to "take it in turns" to allow Lisa to focus on her career. Roger Michell, who directed Penhall's breakout hit, Blue/ Orange (which transferred from the National Theatre to the West End), and then his film adaptation of Enduring Love and Landscape with Weapon, is once again theatrical midwife.

"Women don't particularly want to talk about the visceral nature of the labour and men don't really want to hear about it, so it doesn't get aired," says Penhall, whose plays have traditionally focused on cock-fighting males – from duelling doctors to squabbling brothers. Witnessing childbirth put him in touch with his feminine side. "Men still are, to a certain extent, beefcakes, aren't they? A lot of them are still not in touch with anything inside them. It's scary. I think that men should be made to feel like women."

In the play, Ed's literal embracing of his feminine side gives rise to belly laughs and gross-out humour but it has a serious side. The complications that Ed endures, including a tangled umbilical cord, are straight out of real life and the play takes some hefty swipes at the health service, with medical staff portrayed as rude, absent or incompetent. "Whatever could go wrong, went wrong," he says. "It's quite obvious that we were exposed to a lack of resources." His point is more personal than political, though.

"I wanted to show my wife that I understood viscerally, deep down, the humiliation, degradation, boredom, horror and fear that she'd somehow managed to surf with incredible dignity. So it was partly a kind of present for her but it was also partly because I was curious as to how men would be able to handle it. I was absolutely sure that no man I knew would be able to handle it with the same class and grace as my wife did." How did he handle it? "I was completely traumatised. I was a mess."

His wife, incidentally, is Emily McLaughlin, the artistic associate at the Royal Court who runs the Young Writers Programme, nurturing the theatre's brood of newcomers from debut sensation to the difficult second play. They live in London with a bolthole in Somerset which has no phone, television or internet. Has she read Birthday? "Mmm, yes." And? "I think she likes it. I think she thinks I'm crazy but that it's pretty spot-on, to be honest."

Birthday is Penhall's second play at the Court in the past six months. Haunted Child, about a father who abandons his wife and toddler to join a cult, opened at Christmas. Before that, his last play was Landscape with Weapon at the National Theatre five years ago. In between, he wrote the screenplay for The Road, adapted from Cormac McCarthy's novel about a father and son journeying across a post-apocalyptic wasteland. Fatherhood, it seems, has proved a fertile seam of inspiration. "It definitely lit a fire underneath me." So the pram in the hall is no enemy to art? "I didn't find that at all. I was completely overwhelmed all the time with new ideas, new thoughts. Having children unleashes an elemental fervour in you… I became a completely different animal."

Both plays treat fatherhood with a kind of fascinated, near-primal horror. Birthday even raises the taboo of whether the trauma is worth it. "When it's a difficult birth, there are moments when you think, 'Christ, is it worth all this pain and tension and worry and horror?'," Penhall says. "But also later, when the kids become toddlers, there are still some moments when you think: 'Was this worth it?' And still the horror continues. It's a different kind of horror." Does he worry about his sons reading the play in the future? "No. It's a play about a pregnant man. I mean, come on."

Born in London but raised in Adelaide, Penhall moved to London and worked on the Hammersmith Guardian for four years in the early Nineties, covering everything from murder trials in Shepherd's Bush to Adam Faith playing Alfie in Kingston. In between reporting shifts, he wrote his first play, Some Voices, and sent it to the Royal Court. When Stephen Daldry picked it up, he quit journalism the next day but his plays have always broached, obliquely, the issues of the day, from weapons of mass destruction to maternity services.

He returned to his former profession in Dumb Show in 2004, a black comedy about the boggy collusion between tabloids and celebrities which seems remarkably prescient now. He is, surprisingly, not keen to revisit the topic for the Leveson era. "If I wanted to write about the pervasive corruption and stench that we're talking about now, it would be a much bigger, darker, wilder and more soul-destroying play. But it would be so depressing, you'd just want to shoot yourself."

In case it wasn't already clear, Penhall is outspoken, joyfully so. You won't find him waxing lyrical about the Great British Theatre, its audiences ("Like lambs to the slaughter. You don't have to do much to get a theatre laughing."), or its critics ("They don't get out much, you know?"). In recent years, he has embraced Hollywood, though in typically fractious fashion. He walked away from The Last King of Scotland after a dispute and was ticked off by the Weinsteins for mouthing off about George Bush while promoting The Road.

He's now writing a werewolf film for Ridley Scott and a western for Sam Mendes. An HBO series about an FBI psychological profiler, set in the 1970s and directed by David Fincher (picking up where Zodiac left off) is also in the pipeline. "I love the fact that Hollywood is a massive, muscular machine. There is a narrower focus here. Only a certain kind of film breaks through – royalty films, films about class, secret-agent films. Whereas in America, whatever crazy subject you want to go into – cults, serial killers… – someone somewhere is developing a film about it."

In the meantime, is another play gestating? "Penhall: The Playground Years", perhaps? "I'm exhausted, to be honest. Every time I finish a play, the last thing I want to do is write another. If you get your first play put on at the Royal Court, then a few years later one at the National and it's in the West End for a year, then you're spoilt. It gives you a distorted view of what it's really like for playwrights. Pinter, Mamet, Shepherd, Frayn, Chekhov – they have maybe five classics in a 50- to 60-year career. So as a playwright, you're lucky if you get one, really. But then you think, 'Christ. I've got another four to go.'"

'Birthday', Royal Court Theatre, London SW1 (020 7565 5000; royalcourttheatre.com) to 4 August