Doctors have developed a test to establish whether babies starved of oxygen at birth are likely to suffer brain damage.

Although such brain damage is usually irreversible, they hope the early detection will pave the way for new treatments to prevent it being too severe.

At the moment it can take weeks to see if babies who suffer asphyxia - lack of oxygen - during birth will suffer long-term damage.

The new test could identify the likelihood of the damage within six hours.

Chemical tests

Dr Chao-Ching Huang, of the National Cheng Kung University Medical Centre in Tainan, Taiwan, and his team measured two chemicals in the urine of 40 babies who suffered a temporary loss of oxygen.

They found that six hours after birth, the ratio of the two chemicals - lactate and creatinine - was 186 times higher in the 16 newborns who later developed brain damage than in those who did not.

Oxygen can be cut off during birth by a kink in the umbilical cord or a problem getting oxygen from the mother.

When the oxygen supply is cut off, this can trigger a reaction that causes brain cells to die.

This chain reaction can continue for days or weeks.

Early identification

Dr Jeffrey Perlman, of the University of Texas Southwestern Medical Centre in Dallas, wrote an editorial on the findings, which were published in the New England Journal of Medicine.

He said: "The results are important because they represent an opportunity to identify early, and in a relatively simple way, infants with asphyxia who are most likely to have subsequent brain injury."

This was particularly important, he said, because doctors were about to try out risky treatments to try and reverse the damage, such as inducing hypothermia.

One technique, currently on trial, involves putting a cap full of cold water on a newborn baby's head.

So far, the cooling cap has shown promising results.

However, treatments are still in the early stages and Dr Perlman said the new test would help doctors pick the right candidates for experimental treatments.

"The potential for serious side effects from these therapies emphasises the need for further studies, to ensure that the infants with asphyxia who are most likely to derive benefit are the recipients of these newer interventions," he said.