Infants born at very low weight or more than five weeks early are more likely to become introverted.

According to a new study, published in the journal Archives of Disease in Childhood, children who were born very prematurely or were very underweight at birth are at risk of growing up to become introverted, neurotic and risk-averse adults.

This study focused on about 400 young people and found the group born severely underweight was more socially withdrawn and had trouble making friends and staying in a long term relationship.

Researchers in Germany report that adults born with very low birth weight are more likely to have what they describe as a “socially withdrawn personality.” They are easily worried, less socially engaged, less interested in risk-taking, and more rigid and poorer in communication. Their findings, they say, may explain why people born early or underweight are more likely to have difficulties in their career and relationships. These character traits are associated with people on the autistic spectrum.

The findings follow studies on very low birth weight children, weighing less than 1,500g or born before 32 weeks of pregnancy, which have shown a tendency to lower IQ and autism. But this is the first study to look at the personality of such children in adulthood.

The team, led by Warwick psychologist Professor Dieter Wolke, suggested that these children are likely to be exposed to considerable stresses in neonatal intensive care, which may affect brain development and adult adaptation. “It doesn’t predict the individual. A lot of pre-term children develop normally,” he said.

He said that on the positive side, the very low birth weight babies were less likely to smoke and drink in adulthood, although their reluctance to take risks could set them apart from their adolescent peers for whom risky behavior was part of the normative process of growing up.

“The most important thing is that these are not troublesome children,” he said. “They are just the reverse of conduct disorder children.” The researchers’ work, he hoped, would be helpful to them both at school and at home. “A lot of attention will be paid in school to children who break rules and throw things. These children don’t. They are often forgotten children. They may not concentrate so well. They may not make friends. They are often forgotten and neglected.”

“You shouldn’t solve all their problems for them,” he said. They may need more attention and support in the classroom and to be encouraged to bring other children home for sleepovers, although families should not be overprotective, which can make children more anxious.

The study was part of the Bavarian Longitudinal Study, which has been tracking the health and wellbeing of babies born in 1985-86 in southern Bavaria, Germany. The study involved 200 adults, now aged 26, who had been born very prematurely or with very low birth weight and compared them with 197 others born at term and of normal weight.

Dr Chiara Nosarti, from King’s College London’s Institute of Psychiatry, Psychology and Neuroscience, said, “This is an important study which provides convincing evidence that events that occur early in development contribute to specific aspects of personality.”

“Such information could help in devising targeted interventions aimed at alleviating the impact of a socially withdrawn personality on life outcomes, as the authors suggest, by exploiting neural network plasticity, the life-long process by which the brain adapts to change,” she said.

Dr Nosarti continued, “Future research should focus on providing ‘mechanistic insights’ into the relationship between personality traits and brain alterations in those born premature or with a very low birth weight.”

Professor Celso Arango, president-elect of the European College of Neuropsychopharmacology, called it a very interesting paper. “Personality is an expression of brain function, so if a brain functions abnormally then it will impact on personality. At its extremes, brain development can be sufficiently abnormal as to lead to personality disorders,” he said. “Therefore, it is not surprising that brains exposed to ‘extra utero’ conditions too early, or that suffer other insults perinatally, are more likely to show behaviors that are further away from the mean for the general population.”