Premature babies are more likely to become introverted, neurotic adults and to struggle in relationships and careers, research suggests.
Babies born very early can suffer trauma during medical intervention, which may change the way their brains develop. In addition, parents of premature babies may be more likely to be worried about them, giving them a more anxious upbringing.
Those born before 32 weeks, or weighing less than 3lbs 5oz (1.5kg), are already known to be at a greater risk of autistic behaviour and have generally lower cognitive abilities.
Previous studies have also suggested that those born prematurely could be more likely to be more anxious and introverted, but until now research was unable to say whether these traits were a result of slightly lower intelligence.
The new study suggests the link between premature birth and such personality traits remains true, regardless of cognitive skills.
University of Warwick researchers compared the personalities of 200 young people born very premature or underweight in 1985-86, part of the
Bavarian Longitudinal Study, with another 197 who were born at term in the same maternity units.
The study found those born very prematurely or underweight scored significantly higher for the personality traits of introversion and neuroticism. They were also more likely to report higher levels of autistic spectrum behaviours.
This "cluster of personalities" creates a "socially withdrawn personality", or someone who is easily worried, less socially engaged, less interested in risk taking and less communicative, researchers said.
The study author, Professor Dieter Wolke from the University of Warwick, said: "The higher scores of very premature or low-birthweight adults on the socially withdrawn scale are most likely to be the result of alterations in their brain structure and functioning due to the amalgam of changes in brain development related to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. The physiological circumstances of these babies' births might help explain the higher rates of career and relationship difficulties in adulthood. Babies in intensive care tend to begin their lives in a lot
of pain, with tubes and needles being removed and replaced daily."
Prof Wolke said it was important to analyse these patterns to ensure premature babies lead fulfilling lives. He said: "The evidence shows many find it harder to make friends, find long-term partners and become a parent."