The research was carried out by the University of Bristol

Researchers found that infants born weighing less than 5.5lbs had a 50% increased chance of suffering from or developing psychological distress

They found smaller babies were still prone to suffer from psychological distress irrespective of factors like social class.

The Bristol University research used data from over 5,572 participants.

'Spread panic'

The team from Bristol and the London School of Hygiene and Tropical Medicine examined data charting smaller babies' progress into adulthood, looking at mental development and behavioural problems.

Dr Nicola Wiles said: "This research is useful in enabling us to understand some of the causes of depression.

"We don't want to spread panic with mothers who fear they may give birth to a smaller child but the results were very interesting.

"The findings suggest that low birth rate at full term has a direct effect on adult mental health, rather than simply reflecting a pathway through childhood cognition and/or behaviour."

Previous studies into this topic had found that low birth weight can also increase the risk of children having a lower IQ than their peers at a younger age and of suffering from childhood behavioural disorders.