Babies born to severely overweight mothers have a greater chance of developing conditions such as ADHD, research has found.
Public health strategies that help women planning pregnancies to reach and maintain a healthy weight could help address the risk, researchers say.
Recognising severe maternal obesity as a risk factor could also lead to development of prevention strategies and early interventions to support affected children.
Previous studies have shown that children born to obese mothers face a higher risk of developmental issues such as attention deficit hyperactive disorders (ADHD), and neurodevelopmental problems, such as autism.
Researchers looked at the likely impact on children born to severely obese mothers with a body mass index (BMI) of 40 or above.
They studied symptoms of mental disorders linked to the nervous system in 112 children aged three to five, who had been born to obese mothers.
Those children born to severely obese women had a significantly higher likelihood of hyperactivity, sleep problems and conduct issues, the research found.
They were also more likely to suffer problems such as anxiety, depression and aggressive behaviour, and to have problems linked to development of the brain.
The results, by a team from the universities of Edinburgh, Glasgow and Helsinki, suggest that the risks are higher for children of severely obese mothers. This may mean that maternal weight is a strong indicator for whether children are likely to develop brain-related psychiatric disorders.
The risk remained higher even when other factors were taken into account, such as the mother's mental health, social status, and whether or not she was a smoker.
Conditions such as ADHD and disruptive disorders have a devastating impact on families and are a major public health issue. Some 3.4 per cent of children worldwide are diagnosed with ADHD and 5.7 per cent with disruptive disorders.
Children with these disorders face problems at school and in social situations. Some conditions persist into adulthood.
The research is published in the journal Psychological Medicine, and funded by the charity, Tommy's.
Professor Rebecca Reynolds, of the University of Edinburgh's Centre for Cardiovascular Science and Tommy's Centre for Maternal and Fetal Health, said: "This research underlines the importance of finding ways of helping women plan for pregnancy by optimising their health, including reaching and maintaining a healthy weight."
Article: Prenatal exposure to very severe maternal obesity is associated with adverse neuropsychiatric outcomes in children, Mina TH, Lahti M, Drake AJ, Räikkönen K, Minnis H, Denison FC, Norman JE, Reynolds RM, Psychological Medicine, doi: 10.1017/S0033291716002452, published online 25 October 2016.