For the findings, published in the journal BMC Pediatrics, the researchers studied 368 mothers and their children, all from similar economic circumstances and neighbourhoods, during pregnancy and when the children were 3 and 7 years of age.
"What's striking is, even using different age-appropriate developmental assessments, we found these associations in both early and middle childhood, meaning these effects persist over time," said study researcher Elizabeth Widen from the University of Texas in the US.
According to the study, at age 3, the researchers measured the children's motor skills and found that maternal obesity during pregnancy was strongly associated with lower motor skills in boys.
At age 7, they again measured the children and found that the boys whose mothers were overweight or obese in pregnancy had scores five or more points lower on full-scale IQ tests, compared to boys whose mothers had been at a normal weight.
No effect was found in the girls.
It is not altogether clear why obesity in pregnancy would affect a child later, though previous research has found links between a mother's diet and cognitive development, such as higher IQ scores in kids whose mothers have more of certain fatty acids found in fish.
Dietary and behavioural differences may be driving factors, or fetal development may be affected by some of the things that tend to happen in the bodies of people with a lot of extra weight, such as inflammation, metabolic stress, hormonal disruptions and high amounts of insulin and glucose.
The researchers controlled for several factors in their analysis, including race and ethnicity, marital status, the mother's education and IQ, as well as whether the children were born prematurely or exposed to environmental toxic chemicals like air pollution.
The team also examined and accounted for the nurturing environment in a child's home, looking at how parents interacted with their children and if the child was provided with books and toys.
A nurturing home environment was found to lessen the negative effects of obesity.
According to the researchers, while the results showed that the effect on IQ was smaller in nurturing home environments, it was still there.
Earlier research found lower performance IQ in boys but not girls whose mothers were exposed to lead, and a 2019 study suggested boys whose moms had fluoride in pregnancy scored lower on an IQ assessment, said the researchers.
Because childhood IQ is a predictor of education level, socio-economic status and professional success later in life, researchers say there is potential for impacts to last into adulthood.
The research team advised women who are obese or overweight when they become pregnant to eat a well-balanced diet.
( With inputs from IANS )