When the fat lady sings

"Can you sing down there?" The director Bill Bankes-Jones peers down with fatherly concern at a mezzo-soprano who is lying on her back underneath a table. On top of the table stands a petite soprano, trilling: "I am full of ba-a-a-by!" Four more heads appear beneath her, poking their heads, one by one, out of a gap in the dusty purple velvet curtain that trails off the table and down to the floor. Suddenly, they are all singing at once, jostling for space and crouched on the floor in deafening proximity. A man in a builder's hat and fluorescent jacket strides into the mêlée, breaking off from singing to complain that he has been "clobbered" with too many props - namely, a stepladder, a megaphone and a chainsaw.

This is no ordinary opera rehearsal. But then Push! is no ordinary opera. It is the world's first opera about giving birth, and I am watching the cast labour through scene six. The woman on the table is playing Mary, an IVF patient who believes that she is expecting triplets but is actually expecting quintuplets ("Fifty fingers and thumbs, fifty toes/ Ten ears, ten eyes, five bums to wipe/ Five voices/ One me," she squawks at the discovery). The music director, Tim Murray, leans across from his score to hand me a model of what appears to be a wigwam but is, in fact, a mini-Mary dressed in an enormous, tent-like maternity dress. On stage, Mary's babies will peek out from under her voluminous skirts; for now they must improvise with a table and a curtain.

Mary's is one of six labours and births that make up Push!, the latest production from the experimental opera company Tête à Tête. The eight singers, accompanied by a 13-piece orchestra, will also introduce us to Nimmy, a football fanatic who barely tears herself away from the match to give birth; Cara, a single mother uncertain of who has fathered her child; Maddy, a prisoner who must hand her baby over for adoption; and Angela, whose baby is stillborn. A budding love affair between a maternity-ward cleaner and a hospital porter is interwoven with the extreme comedy and tragedy of these individual scenarios, culminating in the cleaner's own experience of giving birth.

Push! was conceived by the composer David Bruce and the playwright Anna Reynolds for the Genesis Opera Project and was chosen as one of three finalists out of 200 international applications to the scheme. In 2004, Bankes-Jones attended a workshop performance at Sadler's Wells and suggested a full-length production with his company, Tête à Tête.

"It's extraordinary that nobody has written it before. Birth is a thing that makes you go 'aaaaaah'," Bankes-Jones says, pointing out the natural affinity that exists between one of nature's greatest and noisiest dramas and the frequently melodramatic art form. "Operas are always about falling in love and dying, things that make us go to extremes."

Bruce had previously worked with the company on Shorts and Six Pack, two productions that presented six 10-minute operas by six composers in a single evening. His unconventional offerings, Seven Tonnes of Dung ("about a caterpillar, a spider and a dung beetle - a bit of a farce, as you can imagine") and Has It Happened Yet? ("about three old ladies going to watch an eclipse"), were a perfect fit with the company's inventive and irreverent approach to the genre and drew critical acclaim.

Reynolds' play Goodbye Stranger, about a series of one-night stands, acted as the initial inspiration for Push!. "We really liked the idea of a series of stories linked by one common thing, rather than a straightforward linear narrative," the playwright explains. "Since every birth is so different but they all have things in common, it seemed an ideal structure to follow, and David really liked the idea of a series of one-night stands followed by a series of births."

For Reynolds, going from playwright to librettist was a daunting proposition. "With a play, you're left to your own devices and it's your own creation. With this, I would write something and David would say: 'It needs to feel more like an aria here,'" she says. "As the librettist, you're serving the composer, and that's a completely different approach."

"Anna didn't really know anything about opera when she came to the project," says Bruce. "I joke with her now that in some of the early drafts she was putting on an opera voice, a stereotypical idea of what an opera might be."

The finished libretto is sharply written, bitingly funny and touching by turns, and far from stereotypical. At one point, Mary sings sadly: "I always imagined a perfect birth/ Calm, massage, hot towels. Like a first-class plane ride", but Reynolds' research, ("talking to lots of mothers and midwives") confirmed that this is rarely the reality. At times, her libretto takes a disorienting step into the surreal as it explores the inner workings of the women's minds: Mary, giddy and euphoric on gas and air, holds a bizarre conversation with her unborn children; Cara's birthing pool transforms into an underwater world, complete with deep-sea divers; and Nimmy's final push is greeted by a football crowd chanting: "Goal!"

"If I'd been writing for the stage, I would have made things a lot more naturalistic. Opera sometimes needs to be bigger than that for it to work. When you're giving birth, it's a strange and surreal place that you go to," Reynolds says. She is speaking from experience, although she gave birth to her daughter after she had written her libretto. "It's good that we went for the more universal approach, looking outwards. I could have written seven versions of my own experience. Did it resemble Push!? Oh God, yes - bizarrely!"

Bruce, whose wife gave birth for the second time one week into rehearsals, compares the experience to a hurricane. "It's the awe you get from seeing a natural phenomenon. You're dealing with this quite extreme moment in people's lives, which I felt opera was uniquely positioned to convey."

Back in the draughty rehearsal rooms in Islington, London, pictures of Bruce's new arrival are stuck up on the wall with gaffer tape. Bankes-Jones takes a much-needed lunchbreak, apologising to me for "the most anarchic rehearsal so far". Through a mouthful of alfalfa-sprouts-and-tomato sandwich, he admits that Tête à Tête thrives on such chaos. "In a rehearsal room, as you've just experienced, when the people are right up against you, it's much more exciting than when you go to the Coliseum and there's this entity in a costume that you can barely recognise. That's where the name Tête à Tête came from."

The universal subject matter of Push!, he enthuses, is a great way in which to "peddle" new music to a wider audience. Bruce's experimental score, drawing on influences as diverse as Janacek, Stravinsky, Mozart's The Magic Flute and Gluck's Orpheus and Eurydice, is "as extreme as Birtwistle", says Bankes-Jones. "The plan is to let opera be as open to everybody as possible. That's not to say it's not challenging, but it doesn't cut anybody out. It's not intellectual - opera isn't - it's emotional, raw and vulgar."

The atmosphere at Push! is likely to be rather different from the staid, traditional, black-tie evenings at the Royal Opera House, and not just because the flyer promises free tickets to audience members who come dressed as nurses. "I saw the Opera House at its worst a couple of weeks ago. I sat in a posh seat, and around me were all these people falling asleep and leaving at the interval. In the stalls, half of them are interested in what's going on and half are there because it's in between Ascot and Wimbledon," Bankes-Jones says. "Nobody will sleep through Push! - I think that's guaranteed!"

18 to 24 June, Riverside Studios, London W6 (020-8237 1111); then touring to 12 July ( www.pushopera.com)