Premature babies are very susceptible to brain haemorrhaging within their first few days of life because the blood vessels in the head are so fragile.

In most cases, the bleeding is mild and causes no long-term harm. But a severe haemorrhage can result in permanent disabilities, including hydrocephalus or cerebral palsy, or even life-threatening damage to the brain.

Jennifer Brown, whose condition was said yesterday to have "deteriorated", appears to have suffered serious bleeding, which could result in residual brain damage.

Intraventricular haemorrhaging is unusual in babies born at 33 weeks and the problem proves fatal in less than 10 per cent of infants at that age. But specialists say there is a high risk of permanent brain damage, deafness, blindness or motor problems because the brain is still so immature.

Cerebral haemorrhages occur when there is a burst in the network of tiny capillaries, which feeds the brain with blood. They are one of the most common complications in more premature babies. Often there are no outward signs of the haemorrhages, which are graded in severity from one to four. They are usually discovered, as in Jennifer's case, during ultrasound tests of the brain. But the size of the baby means it is very difficult to treat or operate on them.

Dr Nim Subhedar, a consultant neo-natologist at Liverpool Women's Hospital, said babies could be left to recover from mild haemorrhages. "Intraventricular haemorrhages are so common that, unless they are complicated or very large, we don't need to worry about them," he said.

"We don't exactly ignore them, but they are almost standard in premature babies. No surgical intervention is needed because the bleeding goes away in time."

But he added: "In some cases, the haemorrhage stops the fluid in the brain from draining away, leading to a condition called hydrocephalus.

"It is a serious and relatively unusual condition, which requires a surgical operation to drain the fluid."

Dr Subhedar continued: "If a vulnerable, premature baby has a large haemorrhage, a lot of blood that should be in the bloodstream is instead diverted to the brain.

"The circulation can collapse, the heart cannot deliver blood and nutrients to the vital organs and those organs will fail."

The majority of babies who suffered from either a huge haemorrhage or hydrocephalus were left with some degree of disability, Dr Subhedar said.