If your child is born weighing less than a bag of sugar, what are its chances of survival? And what is the price of keeping it alive?
Few could fail to have been moved by Kirsty Cassidy sobbing in court last week as she described how she pleaded with doctors to revive her premature baby, Rebecca. Mrs Cassidy's daughter was born at 23 weeks - lower than the legal limit for abortion. In her evidence to a fatal accident inquiry last week she said her daughter had lived for nearly an hour yet, despite her pleas, Dr Faisal al-Zidgali did not resuscitate the child, saying she was "non-viable" and it would be "futile, heroic and foolish" to try. As the sheriff considers the case, Mrs Cassidy is vowing to fight to make it mandatory that every child born should be helped to live if the parents request it.

The number of babies born prematurely has scarcely altered over the past 50 years, although advances in medical science have made it far more likely that such infants will live. Everyone has heard stories of "miracle" babies who weigh less than a bag of sugar yet manage to survive.

Yet we do not often hear about the other side of premature births, where the risk of death or disability is high. It raises difficult questions: should life be saved if there is only the faintest glimmer of hope? Should expensive intensive-care beds be used for children whose chance of healthy survival is minimal - some 80 per cent of babies born at 23-24 weeks gestation die even with the most intense care. And what happens to families when a premature baby survives but with extensive disabilities?

For Paulette Kane, who gave birth to her son Kieran well before he was due, the case brought back memories of how close she had been to losing him. Kieran was born just short of 26 weeks, weighing 1lb 12oz - and was the size of his mother's hand. When she was taken to hospital with heavy bleeding, Mrs Kane was told to expect the worst. Her consultant told her it would be unlikely Kieran would survive and it was probable he would not be resuscitated if he failed to breathe. It was a terrifying experience for Mrs Kane, who had already lost a baby at 26 weeks.

"I was devastated, but it was a realistic thing for him to say," she said. "It was such a serious thing to take on board, and I was all on my own because my husband was at home with our other child, and I just burst into tears."

She was given steroid injections, which help the tiny lungs of the foetus to mature, and the three days that the doctors managed to stave off birth meant Mrs Kane could be moved to a specialist unit in Cambridge, giving Kieran a better chance. On a ventilator for several days, he survived and is now a happy and perfectly healthy two-year-old.

Nearly 40,000 babies (about 8 per cent of births) are born too soon or too small. One in 150 is stillborn and one mother in four will have a miscarriage. At present, according to Bliss, the charity that supports the newborn, one in 10 babies needs some degree of special care and one in 50 requires intensive care. The degree of prematurity will have a drastic impact on how likely it is that the child will survive. The chance rises from 16 per cent at 23 weeks of pregnancy to 57 per cent at 26 weeks, though at that stage one-third will also be disabled - common problems are cerebral palsy, brain defects and hydrocephalus, pressure from excess fluid on the brain. Just two weeks later, 80 per cent of premature babies have a chance of normal survival.

Parents must realise that the prognosis for premature babies is not always good and there may be a risk of disability, says Dr Simon Bignall, consultant neonatologist at St Mary's Hospital. "We can identify some problems before birth, although not all. We are more or less realistic about what is going to happen although it can be difficult telling the parents, not dashing their hopes but keeping them in the picture, giving them a realistic expectation."

He says, however, that in the past five years there have been dramatic steps forward in keeping tiny babies alive, particularly foetal therapy, where the foetus is given steroids to mature its lungs and, after the delivery, an artificial surfactant - a lung-expanding substance.

But it remains a difficult time for the parents, says Judy Kay, director of Bliss: "One feels a variety of negative emotions: bereaved because the pregnancy did not run to term; guilty, which is totally unnecessary, but mothers often ask, `What did I do wrong?' They often feel hugely vulnerable and, with a baby stuck in an incubator for a long time, bonding can suffer."

Kieran was in care for three months. "I spent so much time in hospital. I was too frightened to leave him," said Mrs Kane. She was helped by the nurses' suggestions that she stroke his body with oil. Ms Kay recommends "kangaroo care", where the baby is allowed to lie for periods next to the naked chest of one of its parents. "The babies get a lot from that technique."

The Office of Health Economics calculated that it cost the NHS up to pounds 70m in 1990 prices (pounds 86.1m today) to provide neonatal intensive care for infants whose birthweights were less than 1,500g (3lb 5oz). Treatment costs about pounds 3,000 a day for the first two weeks, after which it falls to around pounds 600 a day.

An earlier study carried out on Merseyside calculated the amount surviving infants would cost, bearing in mind not only neonatal care but future educational or special needs for those who were moderately or severely abnormal. At today's prices, using those calculations, a baby born with a birthweight of 800g (1lb 12oz) or less would cost up to a quarter of a million pounds.

In "Born Too Soon", a study by Jane Griffin of the Office of Health Economics, Ms Griffin writes: "While compared to the total NHS expenditure the amount on neonatal care for low birthweight babies appears slight, it is important to recognise what opportunities or benefits have been foregone when resources are used for the purpose in question. For example, increased neonatal care resources might mean reduced resources for postnatal support and advice for mothers of healthier babies."

Dr Bignall disagrees: "I don't think it is expensive. Intensive care for newborn infants is very much more cost-efficient than intensive care for the elderly." He added that it was not always possible to make snap decisions: "It can take some time to determine whether the baby will make it or not, what the outcome will be, whether it will have a normal future or not. It is not an easy process.

"We always involve parents in the decision-making process. Most of the time, however, the parents are under a great deal of stress and it is difficult for them to comprehend what is going on as they are unlikely to have a lot of special knowledge."

Dr Bignall's solution is that if there is any chance at all, the medical team will usually resuscitate the baby and then review progress over the first few days. "It is the safest and most pleasant way," he says.

"I expect it cost around pounds 30,000 to care for Kieran," says Mrs Kane. "As far as I am concerned he was worth it. Think of how much we spend on the NHS on people who have smoked all their lives, and then they complain about a few thousands to save a baby's life."

Bliss helpline - freephone 0500 151617