Subtle damage may have a long-lasting effect
Children resuscitated at birth are more likely to have a low IQ by the age of eight, even if they appear healthy as babies, research has suggested.
The study compared babies who were resuscitated at birth - some needing further care, but others not - with those who had a problem-free delivery.
It suggests even mild problems around delivery may be enough to cause subtle damage to the brain.
The study, by Bristol's Southmead Hospital, appears in the Lancet.
It is based on children who were part in a long-term research project known as the Children of the 90s study.
The researchers defined a low IQ as being less than 80.
They found that children who were resuscitated, but required no further treatment, had a 65% increased risk of a low IQ compared with those who were not.
The risk of a low IQ for children who were resuscitated and also required further treatment for signs of brain damage, known as encephalopathy, was six times higher than babies delivered without any problem.
Damage caused during labour is due to the brain being starved of oxygen, a phenomenon known as hypoxia.
Overall the risk of a low IQ for any of the children was still relatively low.
But writing in The Lancet, the researchers said: "Infants who needed resuscitation, even if they did not develop encephalopathy in the neonatal period, had a substantially increased risk of a low full-scale IQ score.
"The data suggest that mild perinatal physiological compromise might be sufficient to cause subtle neuronal or synaptic (nerve cell junction) damage, and thereby affect cognition in childhood and potentially in adulthood."
In an accompanying editorial US experts Professor Maureen Hack and Professor Eileen Stork, of Case Western Reserve University in Cleveland, said the study suggested that better ways were needed to assess whether resuscitation was likely to have a long-term effect on a new-born baby.
These might include biochemical tests, and brain scans.
Andy Cole, of special care baby charity Bliss, said the study was interesting, but did not prove any direct link between resuscitation and low IQ.
He said: "When a very ill baby requires resuscitation there are usually a range of factors at play, including prenatal conditions, the health of the baby at birth, as well as the mother's health.
"It is also important to note that this research is looking at babies born in the early 1990s, and that current resuscitation practices have much improved over the past 15 years.
"The findings may well not be applicable to babies born today."
Professor Andrew Shennan, from Tommy's, the baby charity, said infections contracted by women during pregnancy might be a significant factor contributing to the problems.
He said the study showed that rates of maternal infection were significantly higher in the group with low IQ.
Maternal infections raise the risk of premature birth, which in turn is associated with a higher risk of problems during delivery.