Even a minor oxygen shortage at the time of birth may place a premature baby at higher risk of learning problems later on, say researchers.
It has been known for a long time that babies born early may not score as highly as full-term babies in intellectual and language tests, at least in the first few years of life.
The premature baby’s brain is immature, and may be less able to protect itself from a shortage of oxygen.
However, while severe oxygen deprivation around the time of birth is clearly linked to brain injury, the impact of more subtle deprivation is less well understood.
The small-scale study, from two universities in the US, aimed to provide some answers by comparing the progress of two sets of premature babies - all born at or before 36 weeks - based on a test taken in the first few hours after birth.
This measures the acid levels of the blood, and higher levels are a good indicator that the baby has been starved of oxygen at some point during delivery.
Half of the 52 children had normal blood test results after birth, and half had “mild to moderate acidosis” - a slightly higher reading, but not one usually associated with a longer-term impact.
At the age of six, however, these children scored lower on verbal and “visuospatial” tests than the unaffected children. Researchers described it as “a large discrepancy”.
Dr Sarah Raz, who led the research, said: “Most neonatologists would probably not expect to find a statistically significant relationship between the degree of acidosis measured soon after birth and performance on cognitive tests in pre-school and early school-age children, when acidosis is only mild to moderate at worst.”
The relatively small size of the study means that some experts are likely to remain unconvinced that such apparently minor birth complications could cause such obvious difficulties later on.
So it is unlikely that the research, published in the journal Neuropsychology, will radically change the way that obstetricians and paediatricians approach delivery of premature babies, and their care in the first hours after birth.
Revision date: July 6, 2011
Last revised: by Tatiana Kuznetsova, D.M.D.