The tiniest babies to enter this world are alone at the beginning as they are at the end.

Each sleeps in a humidified crib slung with a blanket, hooked up to monitoring systems, oxygen tubes and catheters no wider than three strands of human hair.

When neonatologist Kei Lui puts his arm through the window of one bassinet, a skinny arm breaks free of its swaddle, reaching into the space like a beetle's feeler, before latching onto the doctor's finger.

None of these babies would survive without modern medicine, but the guidelines that determine which ones to resuscitate and when to administer palliative care are under review.

At 26 weeks, doctors will almost always resuscitate. At 22 weeks, the baby will certainly die.

But those born in "the grey zone" – between 23 and 25 weeks plus six days – live or die at the mercy of their parents, who must decide whether the baby's chance of survival is high enough to justify the trauma of resuscitation, and whether to keep them alive if they are likely to have profound and lifelong disabilities.

The decision must be made ahead of delivery, often with very little time, and doctors have no guarantees as to the baby's prospects, only probabilities.

"We don't have a crystal ball," says Dr Lui, who is the medical director of neonatal care at the Royal Hospital for Women in Randwick.

"Our crystal ball has a bit of colour, a bit of mist and it's not possible to see properly."

The Australian and New Zealand Neonatal Network is planning to depart from conventional wisdom by taking into account the myriad factors that predict mortality and morbidity, rather than rely on gestational age alone.

It will be similar to the risk matrix used in the United States, which takes into account weight, gender, multiple birth status and whether the mother has taken antenatal corticosteroids.

The Australian version would use local data and also consider whether the baby was to be born in a hospital with an intensive care unit.

It will be a useful tool to predict mortality and help counsel parents through what may be the most difficult decision of their lives.

But there will still be a "zone of parental discretion" based on the percentage that it produces.

And it will not replace the internal risk matrix that the parents of these borderline babies must apply to their own circumstances.

For end-of-life care, the cost of keeping somebody alive must be pressed against the sum total of their experiences, the people that they love, their imprint on the world, to reach an impossible estimation on the value of their life. With premature babies this process is performed in reverse. What maythis little person become, and should we give her or him that chance if it could mean condemning the baby to something worse than death?

At what point do our fears clamour out our hopes? What value a human life?

"We're dealing with real people," says Dr Lui. "We're not talking about a product we can reject on the production line. It's hard."

For some people, a 10 per cent chance of long-term damage is too high. For others, a 90 per cent chance of disability is worth rolling the dice.

"The parents have to decide, not for themselves, but for their babies," Dr Lui says. "It's harder than deciding for yourself.

"We have parents who say, 'Yes, resuscitate', but sometimes say later that if they could live through it again they would say 'No'.

"A lot of them choose not to resuscitate but wish they had said yes. 'Maybe I should have given my baby a chance.' There's always a chance of regret."

Margie Parmenter was 23 weeks and five days pregnant when she was admitted to the Royal Hospital for Women with a shortened cervix, whereupon doctors from the Neonatal Intensive Care Unit [NICU] listed the possible consequences of her giving birth to a baby at that age.

"They really did lay out everything in terms of all the potential issues and things that could happen," Parmenter says.

"It was extremely overwhelming. My husband and I were like, 'Oh my God'."

But Parmenter had already lost two babies, both around 18 weeks, and she had already decided that this one would live.

After allowing the information to sink in, the couple decided to keep to the plan. Parmenter was confined to hospital bed rest and they hoped the baby would stick a bit longer.

"The 24-week mark was always front and centre of our minds in terms of viability," she says.

"Both of our previous babies were absolutely perfect – we had full autopsies – it was just the incompetent cervix."

They edged past the 24-week mark and then past the 25-week mark.

At 25 weeks and six days, Archie entered the world weighing just 940 grams – a Goliath for his gestational age. He thrived.

Still not even due to be born until December 3, he has since graduated to the final stage of the intensive care unit and been cleared of neurological damage.

"He's just a normal little baby now," Parmenter says. "I tell you, they're little fighters."

More premature babies are being born in Western countries as a result of older mothers, more twins and more maternal illness, and medical technology means that more of them are surviving.

A major advance occurred in the early 1980s with the advent of antenatal steroids to advance lung capacity.

Until the alveoli are formed  in a baby's lungs about 28 weeks, they breathe through the bronchials, which start appearing around 22 weeks.

When mothers with high-risk pregnancies are given antenatal steroids, the babies' chances of survival from 23 weeks are much improved.

Surfactant replacement therapy has also vastly improved the prospects of preterm infants.

Many babies used to die of lung disease. Now doctors pour surfactant down their wind pipes when respiratory distress is detected, saving countless lives.

Other developments include improved intravenous nutrition, continuous positive airways pressure and specialised maternal foetal care specialists for high-risk pregnancies.

The rationalisation of services in the late 1980s also played a role.

Instead of trying to do everything everywhere, resources are concentrated in big tertiary hospitals.

But prematurity continues to be the most common cause of death in childhood.

There are 247 neonatal deaths in NSW every year, of which 210 are preterm.

Neonatologist Robert Guaran, who is also a board member of the Miracle Babies Foundation support group, says the parents of premature babies are more likely to have depression or post-traumatic stress syndrome a year after the birth.

Parents who have been asked to play judge with their baby's life continue to carry the burden.

"The main thing is giving them information," Dr Guaran says.

"It might be that the family's biggest fear is death, and they want life at all cost.

"For some families their greatest fear is having a child with a severe disability and the impact that will have on the child."

On occasions, neonatologists will override the decisions of the parents, either in choosing to stop administering intensive care when the parents are desperate to continue, or in keeping the baby alive when the parents have decided against.

"I myself probably wouldn't ever do that but some have, because we all act in the best interests of the child.

"The family is the default consenter but nobody owns the child."

Parag Mishra has observed the agony of families from outside and within. He works as a neonatologist at the Royal Hospital for Women and his wife delivered their baby daughter at 29 weeks.

At 750 grams, her birth weight was the equivalent of a 26-weeker, and she had been at risk of an early delivery since 25 weeks.

"It was difficult decision for us because I know that at 25 weeks the chances of neurological outcomes are 50 per cent," Dr Mishra said.

"But the decision to resuscitate or not was completely out of my hands.

His dual responsibilities in the NICU – to his daughter and to his patients – led to some confusion.

Observing him on his tours of the ward, some parents complained that "one of the fathers" was interfering with the other babies.

He gained a new appreciation of what the parents endure, though his own daughter – now a healthy toddler – was robust compared to the smallest babies in the NICU, some of whom weigh just 400 grams at birth.

"It's quite frightening," Dr Mishra says. "It's not a very easy thing for the parents to see."

The babies are born in a foetal position, with their hands and feet together, small enough to fit into the palm of an adult hand.

Even at 23 weeks, they will attempt to breathe and their hearts will beat.

Their skin is so fragile that it will break even if it is stretched a little harshly.

They lose heat and water quickly and these days doctors put them into what looks identical to a plastic freezer bag, though it comes in sterile hospital packaging.

When Margie Parmenter gave birth to Archie it was one of the most anxious and happiest and overwhelming days of her life.

He was obscured at first behind the sheet that is held between mothers and their babies in caesarian operations, then whisked away for the NICU staff to put him into his plastic bag and hook him up to ventilation.

Once he was stable they brought him back in blankets, and she gently touched his face.

"He is just beautiful," she says. "We know that there are going to be ups and downs but we're extremely grateful to be on the road."