A severely ill premature baby who has defied medical expectations by surviving for 17 months should not receive any aggressive treatment, even if necessary to prolong her life, two medical experts told the High Court yesterday.

Although Charlotte Wyatt could see, hear, smile and enjoy being cuddled, her condition remained so serious that it would not be in her interests to be ventilated if it worsened, the court heard. But two other medical experts disagreed and said they would have no objection to the baby being ventilated, as the parents had requested.

Last October doctors won the legal right not to resuscitate Charlotte, who was born three months premature in October 2003, after arguing that she was brain-damaged and "had no feelings other than continuing pain".

Darren and Debbie Wyatt, Charlotte's parents, returned to court yesterday to seek an order requiring doctors to ventilate their daughter if her condition worsens.

Medical experts called by the court agreed that Charlotte's condition had improved, but a paediatrician, Dr H, said she could not envisage a situation where resuscitation and ventilation would be the right course of action.

Charlotte weighed just 1lb and measured only five inches when she was born at St Mary's Hospital, Portsmouth, and has serious brain, lung and kidney damage. Asked about putting Charlotte on ventilation, Dr H told the High Court sitting in Cardiff: "An acute respiratory infection is what would be fatal to her. To ventilate would only postpone it."

She added: "I cannot really envisage a situation where it would be in her interests".

Dr H said Charlotte's general condition had improved, she was more settled, and not in distress. "She does make facial movements but I have never seen her smile, and I have held her, and talked to her and engaged with her. She kicks her legs but she kicks her legs because she can't do anything else I feel, not because she is experiencing any emotion." Challenged by David Wolfe, representing Charlotte's parents, that there had been "quite a dramatic change ... from the situation described unanimously by the medical profession in the autumn", Dr H replied: "Yes. Really the only factor is that she is no longer in distress all the time and needing sedation."

But she added that Charlotte "remains a baby with a number of chronic medical problems". Her brain had not grown since October, the court was told.

Mr Wolfe told the court earlier: "The court certainly cannot say that it will not be in Charlotte's best interests at some unidentifiable point in the future for her to receive treatment. It is sending out a very profound and very wrong message about what we as a society say about disabled people."

Giving evidence via a video-link, another medical expert, known as Dr A, said it was "truly remarkable" that Charlotte had not succumbed to a respiratory infection. But he said this was likely to be because she had not been exposed to an infection rather than because she had survived one. He added: "I think having lung disease as profoundly severe as she has means that if she were ventilated she would suffer from it."

A third expert, Dr G, said there had been a "substantial improvement" in Charlotte's condition. He said: "Certainly I don't think it's unethical to ventilate her; I certainly don't think it would make her life intolerable." A fourth expert, Dr F, said Charlotte had improved but her condition was still "outstandingly severe". Asked if she should receive ventilation if her condition worsened, he said: "I would say, given the circumstances and the parents' wishes, the provision of non- intrusive ventilation would be an entirely appropriate form of care." The case continues.