Children who are born very prematurely are at greater risk of developing mental health and social problems that can persist well into adulthood, according to one of the largest reviews of evidence.



Those with an extremely low birth weight, at less than a kilogram, are more likely to have attention disorders and social difficulties as children, and feel more shyness, anxiety and depression as adults, than those born a healthy weight.



The review draws on findings from 41 published studies over the past 26 years and highlights the need for doctors to follow closely how children born very prematurely fare as they become teenagers and adults.



“It is important that families and doctors be aware of the potential for these early-emerging mental health problems in children born at extremely low birth weight, since at least some of them endure into adulthood,” said Karen Mathewson, a psychologist at McMaster University in Ontario.



Improvements in neonatal care in the past two decades mean that more children who are born very prematurely now survive. In a healthy pregnancy, a baby can reach 1kg (a little more than 2lbs) within 27 weeks, or the end of the second trimester.



The study, which involves data from 13,000 children in 12 different countries, follows previous research that found a greater tendency for very low birth weight children to have lower IQs and autism and more trouble with relationships and careers as they reach adulthood and venture into the world.



It is unclear how a very premature birth, known as a preterm, affects brain development, but children who survive the difficult start are consistently found to be more introverted and risk averse. These factors may drive the more positive tendency to become less prone to drink, smoke and take drugs as adults. The increased risk of mental health problems was seen in very preterm children regardless of where they were born.



Children who were delivered extremely early and weighed less than a kilogram at birth were about four times as likely as those born at term to have attention deficit hyperactivity disorder (ADHD), and significant emotional problems. Those who reached adolescence were twice at risk of these. Adult survivors reported more mental health and social problems, but Mathewson said there are far fewer studies on these individuals.



“This does not mean that, in general, infants born extremely preterm will ultimately develop mental health problems, only that the risk of developing such problems is higher in this group than in those born at full term,” she stresses in the journal, Psychological Bulletin.



Daniel Smith, professor of psychiatry at the University of Glasgow, said the findings were important because mental health issues that occur in childhood are a strong predictor of psychiatric disorders in adulthood.



“There is a strong case for assessing, on a regular basis, the mental health status of these children, so that early intervention approaches might be implemented sooner rather than later, with a view to minimising future mental health problems,” he said. “It is my understanding that children who are born with an extremely low birth weight are routinely assessed for physical health problems in childhood but not currently for mental health problems. This paper suggests that this situation should change.”



Dieter Wolke, a psychology professor at the University of Warwick, said children who weigh less than a kilogram at birth have a “distinct profile” of mental health difficulties in childhood and adolescence. But it was important to note that a third to a half of the children will grow up without any of these mental health problems, he added.



“This study further underlines that extremely low birth weight children and their families need more support to deal with, or to reduce, the adverse effects of ADHD, anxiety and social problems that affect their schooling, being part of their peer group, and being socially integrated. Our own findings indicate that these mental health problems affect wellbeing, wealth and finding a partner and friends who are supportive into adulthood,” Wolke said.



A new EU research programme, coordinated by the University of Warwick, will explore what helps very preterm children overcome the problems they face. Better support for parents and schools, where teachers can learn about the children’s special needs and how to handle their difficulties with attention and making friends, can all help, studies show. “What has been repeatedly noted is that after they leave hospital, they require better liaison of services in the community and with educational services to improve their lives,” Wolke said.