'Birthday' or 'Who's your daddy?'

'Birthday', Joe Penhall

Royal Court Theatre, Thursday 28^th June

It always makes me a tad nervous when the concept of a new play is kept firmly under wraps. It suggests the element of surprise is crucial to a play's success, which rarely bodes well. After all, one sign of a classic play is that you might know the plot inside out but it doesn't mater a jot. In the case of a really good play, exactly what happens is far less important than how it happens, why it happens and the impact of those actions.

The one exception to this rule is a piece of popcorn theatre, such as 'The Mousetrap', which relies heavily on juicy, entertaining shocks to keep its audience enthralled. Otherwise, this secretive approach, in which the plot details are consciously concealed, smacks of uncertainty and hints at a worrying lack of faith in the writer, his (or her) characters, language and ideas.

As it turns out, the key details of Penhall's new play, 'Birthday', can be seen in all their gruesome glory in the trailer, posted on the Royal Court website. As a threatening soundtrack throbs in the background, we see flashes of Stephen Mangan lying in a hospital bed, a huge pregnant belly bursting through his top. 'Birthday', you see, is set in a time when men can give birth just as easily as women. It's a neat concept – but is it anything more than that?

Yes and no. Penhall's play raises some interesting ideas about the ritual and exclusively female humiliation that is childbirth. Watching a prolonged labour on-stage makes you realise just how embarrassing childbirth really is. All manner of objects are shoved up Mangan's bottom, he splays his legs with alarming regularity and his body is essentially no longer his own. Witnessing a man endure this process - under blazing bright lights and in front of a massive, gawking audience – powerfully emphasizes just how brutally exposing childbirth can be.

And yet, for a huge deal of women, pregnancy is an expected and accepted way of life. Does the expectation of childbirth, this play tentatively asks, partly determine a woman's character? Does it make women more compassionate and perhaps more vulnerable? If men were able to become pregnant, would their nature change too? Penhall's exaggerated characters certainly nudge at this notion. Mangan's Ed is an exceptionally sensitive chap, fond of herbal tea and a good old weep. It seems that pregnancy has turned him into a big ol' girl. His wife, Lisa (Lisa Dillon), might as well be a man – she's tough, hot-headed and has a weakness for porn.

These amped up characters make an interesting point about the impact of pregnancy on personality but they're not particularly subtle beasts. Mangan and Dillon's characters begin to feel like punch-line bags. Mangan is a really impressive performer – and his understated comic approach allows him to slide easily into the dark stuff – but he gets lumbered with some tired gags: 'Sex! Is that all you over think about?!' Hell, he even screams out at one point: 'Being a man is much easier. Being a woman sucks!' Yes, yes we get the idea – but what else have you got to say?