Administering general anaesthesia to children under the age of four may affect the structure of their brain and their IQ, the results of a new study suggest.

General anaesthetics are a type of medication that are administered to a person to make them lose consciousness so that they are not aware of surgery being carried out on them.

US researchers looked at 53 children aged between five and 18 who had no history of surgery and compared them to 53 children of the same age who had undergone surgery by the age of four.

All of the participants took part in a language development study, which looked at things like IQ, language skills and listening comprehension.

The researchers emphasised that the average test scores for all of the children were within population norms regardless of whether they had undergone surgery before the age of four or not.

However, they also found that those who had received general anaesthesia before the age of four had a lower IQ and poorer listening comprehension. This appeared to be linked to decreased grey matter in the posterior regions of the brain.

The researchers took other factors into account, such as age, gender and socioeconomic status and none of the children involved had any history of mental illness, neurological illness, head trauma or other potentially related conditions.

According to the study's lead author, Dr Andreas Loepke of the Cincinnati Children's Hospital Medical Center, the ultimate aim of this research is to improve safety for young children ‘who have no choice but to undergo surgery with anaesthesia'.

"It is important to note that no surgeries are truly elective in young children. Many surgical procedures early in life treat life-threatening conditions, avert serious health complications, or improve quality of life. These cannot be easily postponed or avoided," he noted.

He added that despite these findings, current methods of administering anaesthesia are considered very safe and he advised parents who have concerns to discuss these with their doctor.

Details of these findings are published in the journal, Pediatrics.