Excess weight among pregnant women may hinder the development of their babies' brains as early as the second trimester, researchers have warned.
The study, published in the journal Journal of Child Psychology & Psychiatry, linked high body mass index (BMI), an indicator of obesity, to changes in two brain areas, the prefrontal cortex and anterior insula.
These regions play a key role in decision-making and behaviour, with disruptions having previously been linked to attention-deficit hyperactivity disorder (ADHD), autism and overeating.
"Our findings affirm that a mother's obesity may play a role in foetal brain development, which might explain some of the cognitive and metabolic health concerns seen in children born to mothers with higher BMI," said study author Moriah Thomason of New York University in the US.
Previous studies showing an association between obesity and brain development had mostly looked at cognitive function in children after birth.
The new investigation is believed to be the first to measure changes in foetal brain activity in the womb, and as early as six months into pregnancy.
For the findings, the research team examined 197 groups of metabolically active nerve cells in the foetal brain.
Using millions of computations, the study authors divided the groups into 16 meaningful subgroups based on more than 19 000 possible connections between the groups of neurons.
They found only two areas of the brain where their connections to each other were statistically strongly linked to the mother's BMI.
Then, the research team recruited 109 women with BMIs ranging from 25 to 47. (According to the US National Institutes of Health, women are considered overweight if they have a BMI of 25 or higher and obese if their BMI is 30 and higher.)
The women were all between six and nine months pregnant.
The research team used MRI imaging to measure foetal brain activity and map patterns of communication between large numbers of brain cells clustered together in different regions of the brain.
Then they compared the study participants to identify differences in how groups of neurons communicate with each other based on BMI.
The investigators cautioned that their study was not designed to draw a direct line between the differences they found and ultimate cognitive or behavioural problems in children. The study only looked at foetal brain activity.
But they now plan to follow the participants' children over time to determine whether the brain activity changes lead to ADHD, behavioural issues, and other health risks.