Babies born very premature or severely underweight are at heightened risk of becoming introverted, neurotic, and risk averse as adults, indicates research published online in the Archives of Disease in Childhood (Fetal & Neonatal Edition).

This personality profile may help to explain the higher rates of career and relationship difficulties experienced by this group as adults, suggest the researchers.

Very premature birth at less than 32 weeks and/or very low birthweight of less than 1500 g are known to be linked to a heightened risk of autistic spectrum behaviours, but it has not been clear if prematurity and low birthweight might affect other adult personality traits.

The researchers therefore compared the personality traits of 200 26 year olds who had been born very prematurely and/or severely underweight with those of 197 young people who had been born at term and within the normal weight range.

They wanted to find out if there was a distinct personality profile linked to extreme prematurity/low birthweight, and if lower IQ--which is associated with very early birth-- explained any personality differences.

Study participants were either part of the Bavarian Longitudinal Study, which has been tracking the health and wellbeing of children born in 1985-6 in Southern Bavaria, Germany, and admitted to hospital within 10 days of birth, or those born at term in the same maternity units over the same timeframe.

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Personality traits were assessed at the age of 26 across five dimensions: introversion; neuroticism (tenseness and anxiety); levels of openness to new experiences; agreeableness; and conscientiousness.

Adults who had been born very prematurely and/or extremely underweight scored significantly higher on all but two of the personality traits--conscientiousness and openness--than their peers born at term.

Taking account of potentially influential risk factors did not alter the magnitude of these differences.

Adults who had been born very prematurely and/or extremely underweight also reported significantly higher levels of autistic spectrum behaviours, introversion, neuroticism, agreeableness and lower levels of risk taking.

The personality traits that best described the profile of adults who had been born very prematurely and/or extremely underweight were: introversion, risk aversion, autistic spectrum behaviours and neuroticism. The findings held true even after taking lower intelligence into account.

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This cluster of traits describes a 'socially withdrawn personality,' or someone who is easily worried, less socially engaged, less interested in risk taking, and less communicative, say the researchers.

"The higher scores of [very premature/low birthweight] adults on the socially withdrawn scale are most likely to be the result of alterations in their brain structure and functioning due to the amalgam of changes in brain development related to premature birth and prenatal and neonatal insult," write the researchers.

They go on to suggest that these children are likely to be exposed to considerable stressors in neonatal intensive care, which may affect brain development and adult adaptation, added to which early birth may prompt parents to be over protective.

The physiological circumstances of these babies' birth might help explain the higher rates of career and relationship difficulties in adulthood, say the researchers.

The evidence shows that many adults born very premature/low birthweight are less likely to go on to higher education or get well paid jobs; and they find it harder to make friends, find long term partners, and become a parent, the researchers point out.