The study, conducted by Alina Rodriguez at the Uppsala University in collaboration with international colleagues, examined 12,500 children and found a correlation between the mothers body mass index (BMI, weight in relation to height) at the time she became pregnant and symptoms like hyperactivity and concentration problems in the child.
"Many children are being diagnosed with ADHD and at the same time there is an epidemic of obesity in the world, with more and more women already overweight at the time they become pregnant," Rodriguez said.
"If it turns out that the mother's weight is of significance and, together with other factors, can influence ADHD-like symptoms in the child, we have not only found a contributory cause but also a potential avenue for preventive work that can enhance the well-being of both mother and child," she added.
In the study, the children were monitored from their time in the womb up to school age, when their teachers were asked to answer a questionnaire about the child's behaviour.
The analysis found that roughly one out of ten children had marked difficulties with their attention span and with hyperactivity.
"How many of them actually have ADHD cannot be determined solely on the basis of the questionnaire responses, however," Rodriguez said.
The link between mothers' body mass index and child symptoms was also found in cases where the women were moderately overweight.
Expectant mothers who were already overweight and moreover gained a considerable amount of weight during the course of the pregnancy ran a greater risk of having a child who would later show signs of ADHD than did women of normal weight who experienced the same weight gain during pregnancy.
"It is important that women start off pregnancy at an optimal body weight. It has been well documented in recent years that mothers overweight is associated with increase risk for a number of complications both to herself and to her child. Our results could be yet another problem to add to the list. But it is not good to be extremely thin either," Rodriguez said.
The study is issued online in the International Journal of Obesity.