The brains of very premature babies may be damaged by the use of steroids to prevent and treat chronic lung disease, research suggests.
Premature babies lungs are vulnerable
Researchers from the Royal Hospital, Belfast, found babies who had been given steroids showed signs of impaired brainpower as children.
They say the benefits of the drug must be balanced against possible longer term damage.
The study was presented at the British Psychological Society annual meeting.
The researchers compared 77 premature children who were treated with postnatal steroids with 66 premature children who did not receive the drugs, and 25 siblings who were not premature.
The results showed that the children who were treated with steroids performed less well on a range of tests designed to assess eight areas of mental ability.
However, the researchers stress that steroids have been shown to be an effective way to treat chronic lung disease, a common problem in premature infants, who are often born before their lungs are fully developed.
The drugs prevent inflammation of the infant's delicate airways and aid their development, allowing the babies to come off ventilators and be discharged from intensive care more quickly.
Lead researcher Trevor Wilson told BBC News Online: "Steroids are given because they are very powerful drugs with a powerful anti-inflammatory effect.
"However, there are many steroid binding sites in the brain, particularly in the hippocampus, which plays a major role in memory.
"My advice to doctors would be not to use these drugs unless the child is very sick and not likely to survive without them."
However, Mr Wilson said his research had also shown that a loving, supporting home life could go some way to negating the negative effects of steroid use on the brain.
The new research echoes the findings of a US study published in the New England Journal of Medicine last month.
Doctors at the China Medical University in Taichung found babies given a potent steroid called dexamethasone were more likely to have a lower IQ and poor motor skills.
Lead researcher Dr Tsu Yeh said: "This therapeutic regimen should not be recommended because of its adverse effects."
Professor Henry Halliday, an expert in neonatal respiratory medicine at the Royal Maternity Hospital, Belfast, said previous studies had also raised concerns about the use of steroids in the first few days after birth.
However, he said the new research was possibly the first to provide evidence of a long-lasting impact on mental function.
Guidelines issued by US and European bodies now cautioned against using steroids in the first two or three days after birth, he said.
"If you wait until the baby is a week old before giving steroids there is evidence that this reduces the risk of chronic lung disease and improves survival rates, but no evidence that it causes long-term harm to development," he said.
Dr David Field, convenor of the British Association of Perinatal Medicine, told BBC News Online, that the use of steroids to treat premature babies had declined hugely over the last decade.
"There is a fair amount of evidence to suggest that steroids do have an adverse effect on development," he said.
"However, no everybody is convinced. Some people suspect that as these children are very sick anyway one would expect to find problems in their subsequent development."