When Nicola Roberts was pregnant she had to stop work in her fourth month: as a soloist with the Royal Ballet she had been cast to dance one of the animals in Tales of Beatrix Potter and the role was too dangerous. 'I had to wear a mask, which meant I couldn't see or breathe properly, and I had all these stairs to run up and down.'

Lauren Potter, a freelance contemporary dancer, continued performing until the end of her seventh month, but she had a problem with other people's efforts to be kind. 'Everyone kept trying to stop me moving the scenery,' she says, 'by giving me extra dancing to do instead.' For the performance she was rolling on the floor, jumping into people's arms and working her body at full stretch. Her mother sat through the show with her eyes shut.

A dancer's work is her body, and Potter's nerve is exceptional. For dancers, ballooning breasts and swelling stomachs are not only irritating, but potentially disabling - making it difficult for them to lift or stretch their limbs, affecting their balance and strength and preventing their getting into costumes.

For some, the loss of control can be traumatic. From childhood, a dancer is used to exercising daily vigilance over her body. Her greatest professional pleasures are when her limbs do exactly as she wants, her greatest pains come from the mirrors that expose her imperfections. For a ballet dancer the desired look remains the hipless, breastless adolescent. A lucky few achieve this without constant dieting (though anorexia remains a professional hazard), but none comes through the system without feeling vulnerable about how she looks.

All this can make pregnancy particularly disorientating. Dancers have to accept that their hormones have taken control of their bodies, plumping out flesh, softening joints and perhaps causing varicose veins or piles. They also have to deal with the fact that in this competitive profession they will be out of the race for a year, with no guarantee that they will revert to their old lean and hungry selves.

When Tracy Brown, another soloist with the Royal Ballet, became pregnant she felt 'very frightened'. She had always had a 'struggle with weight' - as her body started growing and she felt her dancing 'slipping away' from her, she began to panic. When she found herself sobbing outside the rehearsal studio she knew she had to stop working.

Only then did she 'really start enjoying being pregnant'. This included eating three meals a day (unheard-of for dancers) and putting on three stone in weight.

Even when pregnant dancers are forced off the stage, it is rare for them to abandon daily class. The routine is an addiction. In any case, they can't afford to sink into a chocolate-munching torpor. If most ordinary women are nervous of their weight going ballistic and their muscles turning to flab, dancers can't even afford to think about it.

Dancers tend to look sleek and glowing in their late pregnancies, their bumps taut with muscle tone, but they are notorious for having difficult labours: tough muscles can often fail to relax efficiently. Brown says that every time she pushed the baby out 'he seemed to get sucked back in'. She also admits that none of the pain she had endured as a dancer prepared her for the ruthlessness of contractions.

Fiona Chadwick, principal dancer with the Royal Ballet, had a hard time when she gave birth, too - 24 hours followed by an emergency Caesarean. Lauren Potter's labour was less arduous. She thinks that being a dancer at least helped her to follow the midwives' instructions. 'I know my body and I'm used to doing what I'm told,' she grins.

After the birth, a dancer can't hang around in a state of loopy postnatal bliss. Most give themselves less than six months to get their bodies back into a tutu. Chadwick surprised even herself by returning to class five weeks after her Caesarean.

Brown admits that it was hard shedding the weight. It was a year before she 'felt really good about being in a tutu'. But both found that maternity leave gave them a welcome chance to retrain their bodies, and they believe their dancing improved as a result.

The worst experience was waiting to see whether they'd return to their old roles, knowing that others had been performing, perhaps brilliantly, in their place. There is little sentimentality in the ballet hierarchy and a dancer is only as good as her last season's performances. Though Roberts hasn't even had her baby yet, she is already dreading 'waiting for the cast lists to go up for the autumn'.

In fact the Royal Ballet has so far been generous to returning mothers and both Chadwick and Brown went back to dancing major roles.

Things are tougher for Potter, in the world of independent dance. She has to decide if she can actually afford to go back to work. Dancers are so poorly paid, she says, 'that with child care for Molly I'll probably be paying to work'.

Despite the problems, a baby boom seems to be beginning in the world of dance. 'When I first joined the company,' says Brown, 'dancers who got pregnant just left.' Recently, though, she and her husband, the dancer Christopher Saunders, took their 13- month-old son on tour to America. 'People seemed to love him being around,' says Brown. 'I think it gave them a sense of normal life.'

Chadwick is even more positive, in spite of broken nights and 'dashing around' to make time to spend with Emily. 'Having a baby gave my dancing a new lease of life,' she says. 'I felt much more confident and I seemed to have so much stamina, I felt like superwoman. I suppose having babies is what women are designed to do.'

Tracy Brown dances in 'A Month in the Country' on 1 August. Fiona Chadwick dances in 'Don Quixote', 30 July, and 'Romeo and Juliet', 6 August. (All at the Royal Opera House.)

(Photograph omitted)