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The researchers said that given the size and power of the trial, it is justifiable to conclude it shows evidence of IQ equivalence between the groups.

New research carried out in collaboration with the University of Birmingham has found that giving young babies a general anaesthetic has no lasting impact on their brain development or behaviour.

The study, published today in The Lancet, looked at the effects of having surgery under an ‘awake’ local anaesthetic, compared to an ‘asleep’ general anaesthetic in 722 babies at 28 hospitals across seven countries.

The infants were all aged less than 60 weeks and underwent hernia operations (inguinal herniorrhaphies) between 2007 and 2013 in hospitals in the UK, US, Australia, Italy, Canada, the Netherlands and New Zealand.

Almost half the group (361 babies) received a localised anaesthetic which saw them remain awake, while the other half (359 babies), had a general anaesthetic which meant they were asleep.

Five years later the children were given a formal IQ test and there was no sign of any difference between the two groups. The children also underwent a series of behavioural, memory and attention assessments, and again there was no difference between the two groups.   All the children were tested within four months of turning five.

The researchers said that given the size and power of the trial, which was supported by the National Institute for Health Research (NIHR), it is therefore justifiable to conclude it shows evidence of IQ equivalence between the groups. 

Pollyanna Hardy, of the University of Birmingham’s Clinical Trials Unit, who led the study’s statistical work, said: “The reason the children were tested at the age of five is important because there is robust evidence that this is the age when their general intelligence is apparent and their IQ will unlikely change even into adulthood.

“It has also been shown that IQ aged five years is highly predictive of later maths ability, and that higher IQ in childhood positively predicts a range of benefits in academic, economic and health outcomes across the lifespan.”

Corresponding author Professor Andrew Davidson, of the Murdoch Children’s Research Institute and the Department of Paediatrics at the University of Melbourne, said: “The research focused on very young babies because early infancy is a known to be a period of ‘high cerebral vulnerability’, when the brain is rapidly changing and developing.

There are many animal studies that show anaesthetics can affect brain development and several previous human studies have found a link between surgery in childhood and later behaviour problems or poorer academic achievement, but these human studies may be flawed due to inherent bias.

“Babies who have surgery often have other conditions which may explain the later issues,” Professor Davidson said. “The only way to try to see if the anaesthetic is causing a problem was through such a trial.”

The five-year IQ follow-ups were carried out between 2012 to April 2018 using the Wechsler Preschool and Primary Scale of Intelligence – Third Edition – Full Scale IQ.

The behavioural assessments were the Wechsler Individual Achievement Test Second Edition (WIAT-II) or the BVN (the Italian equivalent of the WIAT-II), selected subtests of the Children’s Memory Scale (CMS), the Global Executive Composite (GEC) of the Behaviour Rating of Executive Function – Preschool Version (BRIEF-P), the Adaptive Behavioural Assessment System Second Edition (ABAS-II) and the Child Behaviour Checklist Caregiver Questionnaire (CBCL).