In contrast, the research results found that the IQ of adults who were born full-term could not be accurately predicted till the age of six.
Previous studies have linked very premature birth and very low birth weight with impaired cognitive function from childhood and throughout adulthood.
However until now it wasn't clear how soon adult IQ can be predicted in these children.
"We believe this is the first time a research paper has looked into the prediction of the IQ of adults over the age of 26 who were born very premature or with very low birth weight," said Dieter Wolke, professor at the department of psychology and Warwick Medical School, University of Warwick in UK.
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Across all assessments within the study very premature and very low birth weight children and adults had lower IQ scores than those born full-term, even when individuals with severe cognitive impairment were excluded from the comparisons.
The study was conducted in Germany and followed children from birth into adulthood who were born between 1985-86.
The data gained on cognitive function were assessed with developmental and intelligence tests (IQ) at five and 20 months and at four, six, eight and 26 years of age.
Their results were not sex-specific, related to income or education, and were compared to the control group of adults who were born healthy in the same obstetric wards.
"Some children born very premature or with very low birth weight score low on cognitive tests but beat the odds and improve into adulthood," said Wolke.
"However many with persistent problems can be detected in the second year of life," he said.
"Early identification of cognitive problems in these children may help to plan specialised therapeutic and educational interventions to help them and their families," Wolke added.