The study published in the American Journal of Epidemiology saw a comparison between eight-year-old children and found that kids of mothers who ate large amounts of liquorice when pregnant did not perform as well as other youngsters in cognitive tests on vocabulary, memory and spatial awareness.
Sixty-four of the children who took part in the study were exposed to high levels of glycyrrhizin in liquorice, 46 to moderate levels and 211 to low levels.
Behaviour was assessed using an in-depth questionnaire completed by the mother and also used by clinicians to evaluate children's behaviour.
The research concluded that women who ate more than 500mg of glycyrrhizin per week - found in the equivalent of 100g of pure liquorice - were more likely to have children with lower intelligence levels and more behavioural problems.
Some of the inadequacies in the kids, selected from Finland where consumption of the drink among women is common, were poor attention spans and ADHD (attention deficit hyperactivity disorder).
The study, carried out by the University of Helsinki and the University of Edinburgh, suggested that a component in liquorice called glycyrrhizin may impair the placenta, allowing stress hormones to cross from the mother to the baby.
Apparently, high levels of such hormones, known as glucocorticoids, affect fetal brain development, which leads behavioural disorders in children.
Professor Jonathan Seckl, from the University of Edinburgh's Centre for Cardiovascular Science, said: "This shows that eating liquorice during pregnancy may affect a child's behaviour or IQ and suggests the importance of the placenta in preventing stress hormones that may affect cognitive development getting through to the baby."
Professor Katri Räikkönen, from the University of Helsinki's Department of Psychology told: "Expectant mothers should avoid eating excessive amounts of liquorice."