Three Women, Jermyn St Theatre, London<br>Showstopper! King's Head Theatre, London

A forgotten radio play by Sylvia Plath captures the diverse universes into which women are propelled by pregnancy

Love and her naughty little brother lust are leading characters who bestride the stage most nights, but lactation rarely gets a look-in. Shakespeare prods at a dug or two, but thereafter the process of keeping the new generation alive is not deemed the stuff of drama. Sylvia Plath, however, raises her distinctive voice on the ever-topical subject in a play being given what is thought to be its first professional staging for 20 years.

Three Women, published in 1962 and performed on radio that year, crystallises the experiences of three pregnant women – one who ripens blissfully to childbirth and post-natal infatuation, one who miscarries and tries in vain to conceive anew, and one who gives up her baby girl for adoption. In turn, they articulate the hopes, fears and essential separateness of the woman who carries, or dreams of carrying, a new life.

"I cannot help smiling at what it is I know," contemplates the beatific madonna, played with Juliette Binoche-like serenity by Elisabeth Dahl. "Leaves and petals attend me. I am ready." Soured by disappointment, by contrast, Tilly Fortune grieves as her baby bleeds away, and again every month, exasperated by all that is flat, empty or dessicated as she yearns for a big belly instead of her smart office tailoring: "I lose life after life. The dark earth drinks them."

Finally, while the first mother oozes rivers of milk, the woman who must give up her child – abortion being only a dangerous and illegal option at the time of the play – returns to her studies, mourning in her academic gown. Lara Lemon, resigned to her loss, has a melancholy beauty – but possibly the most sketchily drawn role.

Robert Shaw, who spent two years negotiating the rights to stage Three Women, knows that the colours are best on radio: the text is striped with the rainbow hues of the nursery, so Lucy Read's set is monochrome, studded with ghostly, fossilised baby things and a startling blue shaft of moonlight. The whole is like a thought bubble hanging over the more common picture of family, the circus of new shoes, homework and spaghetti.

Three Women is heart-rending but, for tears of laughter, go to the King's Head and an evening of organised mayhem. To launch headlong into an improvised musical is the artistic equivalent of addressing a school speech day with no clothes on. Showstopper!, created every Monday night, kicks off with a troupe of bright sparks ready to dazzle at one side of the stage, director Dylan Emery standing by with two other musicians at the other, and, out front, an audience bursting with suggestions for material.

The result is a joyous, uproarious collaboration propelled by the quickwittedness of the multi-talented cast and their mischievous onlookers. Emery gathers in the audience's suggestions: parody songs must be in the style of Sondheim, Bernstein, meaningless anthems à la Lloyd Webber, and Bob – "Marley or Dylan?" checks Emery. Marley wins by a mile, and cues the extemporary hit of the night – a reggae number for a Peruvian mystic (Adam Meggido) and a 19th-century apothecary (Alan Marriott) who cannot cure himself.

You get the picture: for sheer madcappery, refreshingly wholesome, good-natured musical slapstick, The Sticking Place's musical high-wire act is hard to beat. Who knows what they'll come up with tomorrow night?

'Three Women': Jermyn St Theatre, London SW1 (020-7287 2875) to 7 Feb. 'Showstopper!': King's Head, London N1 (0844 412 2953) Monday nights until 2 Mar