Alexia Pearce looks at her three-year-old son Nathan every day and feels the same rush of guilt. Guilt that she chose to let him live when he was born too early, just 23 weeks into her pregnancy. "If I'd known then what I know now about what extremely premature babies have to go though, I would not have chosen that for my little boy.

"I would have wanted them to give him to me and for him to pass away in my arms. I find the whole issue of what he has been put through, what he continues to be put through, very difficult. I feel very guilty that I took that decision, postponing the inevitable."

Nathan still faces a premature death because of the range of his conditions and disabilities. He had to have 22 blood transfusions in his first three months of life, just to replace the blood that was taken from his tiny body for tests. Like all extremely premature babies, he had to be given a cocktail of drugs to support his underdeveloped lungs and other organs, one of which kept his heart safely sealed but as a side-effect left him profoundly deaf.

"He can't walk or talk. He's oxygen dependent, although hopefully that might change. He has chronic lung disease, cerebral palsy and global developmental delay. He has diabetes inspidus and his thermostat is a bit wonky so he gets hot and cold."

It is, says Pearce, a great taboo to wonder if she should have let her son go when he was born so fragile and weak, but one that she feels strongly that she should break. "More people need to be aware of what these little chaps go through," she said.

"He was there with lines coming out of his arms, needles in every limb and his abdomen, but by then it's too late to go back. You can't just say 'Switch off the machines and give him to me, let him go, stop this'. I felt it, though, I still do. You're damned if you do and damned if you don't.

"I have no regrets that what has happened has happened. Now this most gorgeous little thing is here and I absolutely adore him. I am so glad I have got to know him. But that doesn't stop me knowing that all I have done is postpone the inevitable. He's not expected to live a very long life. I don't think he'll make it to his teens. He's so frail.

"I do feel guilt over the choice I have made, even though it's all done with the best intention. No mother or father wants to see their child suffer. Because of the choices I have made I feel he has suffered, and still does."

Around 8% of British babies are born prematurely, compared with 13% in the United States. A premature baby is defined by the World Health Organisation as an infant born before 37 weeks of gestation. Of those babies, 93% will be born over 28 weeks, with good chances of survival but a one in 10 chance of being left with a permanent disability such as cerebral palsy, blindness or deafness.

For those, such as Nathan, who are born earlier, the odds are far, far shorter. And with the numbers of over-45s having babies doubling in a decade and IVF multiple births also on the rise, premature babies are becoming more common.

While the latest figures show that 39% of babies born at 24 weeks are now surviving with help from medical advances, the chances of those children suffering no serious ill-effects in later life are low – around six in 100. Last year, researchers from University College Hospital, London, found that premature babies were more sensitive to pain. All pre-term babies are more at risk of a lower IQ, poorer cognitive functioning, learning disabilities and behavioural problems such as attention deficit disorder than full-term babies.

It makes the area of where to draw the line a difficult one for medical professionals. Dr Bob Welch, neonatal consultant at the Royal Shrewsbury Hospital, said: "It's uncomfortable for all of us, all of the time. When I first started in this area in 1980, basically babies born at 28 weeks weren't even looked at as possibly viable. Now you expect most babies born after 26 weeks to survive and survive quite well.

"But you are always saying 'Am I doing the right thing?' Personally, I don't like resuscitating before 24 weeks, but at the end of the day it's what the family want. Some will accept the inevitable, and some will want to push on. Likewise with the babies. Some come out screaming and demanding to live, others are much more lifeless. Many survivals will come at a cost, but of course all parents are hoping their baby is the one who beats the odds."

For Pearce, Nathan is a much-loved part of her family, a family that against the odds has managed to stay together. She was moved to talk about her situation after watching a BBC2 documentary earlier this month that provoked questions about the resources being poured into neonatal units.

"I can't come at it from an NHS financial point of view, but I come at this from a human cost point of view," she said. "My other little boy is amazing with Nathan. He can always make him laugh and he wants to help care for him, helping to bathe him and change his nappies. It has made him a very kind little boy. But I never wanted him to go through this either. One day he had a full-time mum and the next I'm at the hospital all the time. He's coped with it so admirably so far. Our lives just changed so dramatically; that's the human cost."

Statistics show that many marriages founder under the strain of having a disabled child and of mourning for the child that was expected, but Pearce and her husband have managed to come through it together. "There's no question that you put your relationship last; your focus is on your children and it's tough.

"You hear about 'miracle babies' or 'little fighters' and people have such a romantic view about premature babies – 'Oh, there's an incubator for a little while and then they go home and everything is rosy'. It's not."

"Obviously every life deserves a chance, every life. But you wouldn't put an adult through that. You wouldn't put an animal through it. If an adult required that level of medical intervention then someone would be taking the family aside and suggesting gently that the machines are switched off."

Pearce had no warning of her own premature birth, brought about by a sudden complication in the pregnancy, a placental abruption, and had none of the risk factors – she doesn't drink or smoke, isn't obese and her first son, Dominick, now five, was born at full term.

"You're in pain, you're bleeding, you're at the hospital and they whirl in, you get a chat, they're talking to us about statistics but none of it is getting through to my mind and you are like a rabbit in the headlights. All I could say was if he comes out and he's not looking good, let him go. But if he comes out looking as though he is up to facing the process, and at that stage I had no idea what those processes would be, then please save him. My key thing was suffering. That was the only thing I was sure about in my head. They said 'No, no, he won't suffer' but I know now that's not true: they do suffer."

She is keen to stress that she feels no resentment over the way she was treated by the medical staff. "I'm not saying the doctors were gung-ho about it, they weren't at all. I think they all have the same questions about what they are doing every day: 'Are we doing the right thing? Just because we can, should we?' "I was treated with the utmost dignity and respect. So I don't feel betrayed in any way, but I feel it was obvious what the outcome would be. I remember when I was taken to the incubator to see him for the first time. I was howling and wailing, I thought it was so unnatural, so hideous, it didn't look right. When you give birth, it's a natural process and this wasn't like that.

"Birth and death are the most natural processes a body can go through and Nathan's birth and treatment was so far removed from that. Strange birth, choices to be made, difficult bonding. I had to wait six weeks to hold my son and when I did he was still attached to a ventilator and I had many nurses around me. It was all so clinical."

An advocate or counsellor figure would, she feels, help the mother think more clearly about the situation.

"I am not saying that I think pregnant women should be deluged with information about it," she said. "These days you get so much information that there is already so much to be paranoid about. It's a fine balance, overloading pregnant mums – after all, you can't prevent a premature birth.

"I had so many people coming in and out, you're in a haze. I think it would be helpful if there had been an advocate. When we got a counsellor a few days after the birth it saved my sanity."

Andy Cole is the chief executive of the charity Bliss, which campaigns on behalf of premature and sick babies. He said: "The decisions facing parents of these very tiny babies are extremely challenging. Sadly, most 23-week babies will not survive, but a significant number do. Doctors and nurses provide amazing care to these vulnerable babies. However, we know that around 50% of units do not provide counselling to their parents. It is crucial that families receive the support they need at this incredibly difficult time."

But for Alexia Pearce, it's important for families to fully understand too that the difficult times do not end when the baby leaves the incubator. "When you go into labour that early, nobody is a winner," she said. "I'm not saying stop people from having their premature baby resuscitated. I'm not saying babies shouldn't be saved. I am saying that the myth that there is a happy ever after needs to be explored and it's important that we talk about it.

"Science is moving on so fast but until we can invent an amniotic sac, there is a big cost to these babies and nature is still against their survival."