The study of more than 1,000 children found that the offspring of obese mothers had a 67% higher risk of autism than the children of normal-weight moms, and more than double the risk of having developmental delays, such as language impairment.
"The odds of autism and other developmental delays were significantly higher in the children of moms who were obese versus those who weren't," said lead study author Paula Krakowiak, a biostatistician and doctoral candidate at the University of California, Davis.
The research included more than 500 children aged two to five with mild to severe autism, about 170 children with another type of developmental disability, and 315 typically developing children, all taking part in the Childhood Autism Risks from Genetics and the Environment, conducted between 2003 and 2010.
How the study was done
Children were assessed by experts from the university's MIND Institute to confirm their autism diagnosis, while mothers were interviewed about various aspects of their health before and during pregnancy. Information about weight came from either medical records or mothers' recollections of their weight before and during pregnancy.
Obesity is defined as a body mass index of 30 and up. Body mass index, or BMI, is a measure of body size based on height and weight.
While diabetes was also associated with increased odds of developmental delays in offspring, there wasn't a statistically significant association between diabetes and autism. The research is in the journal Pediatics.
Autism is a neurodevelopmental disorder in which children have difficulties with social interaction, verbal and nonverbal communication such as reading facial expressions and understanding other social cues, and restricted interests and behaviours.
About one in 88 US children has a so-called autism spectrum disorder, which includes milder forms of the disorder, such as Asperger syndrome, according to updated figures from the US Centers for Disease Control and Prevention. One in six US children has a developmental delay, such as a speech or language impairment or other intellectual disabilities, the CDC says.
Considering that about one-third of the women of child-bearing age in the United States are obese and almost 9% have diabetes, the findings could have serious public-health implications, said Krakowiak.
Findings are important
Dr. Andrew Adesman, chief of developmental and behavioural paediatrics at the Steven and Alexandra Cohen Children's Medical Center of New York, said the findings "should not be ignored". However, he noted that other genetic or environmental factors are likely contributing to autism. Many parents of autistic children are of normal weight, while many obese parents don't have autistic kids.
"Although the results of this study suggest obesity is a risk factor for developmental problems in offspring, one cannot assume that developmental problems in the offspring are due to obesity, and many other factors may be involved or responsible," Adesman said.
Indeed, other research published last week identified several spontaneous genetic mutations as the cause of a fraction of autism cases. Parents' ages, especially fathers older than 35, were also associated with autism in those recent studies, published online in the journal Nature.
The reasons for the link between obesity and autism/developmental delays are unknown, though some research suggests that obesity unleashes inflammatory proteins, some of which may be able to cross the placenta into the foetus. It's possible the inflammatory proteins, known as cytokines, may harm a foetus's developing brain, Krakowiak said.
She also noted that while the research found an association between obesity and autism/developmental delays, it did not prove that being obese causes autism or other brain problems in the foetus. The link may be indirect.
"It may not be the obesity itself, but other things that lead to obesity, such as genetics, or lifestyle, or diet," Krakowiak said.
Hypertension in pregnancy also a risk
About 24% of moms who had a child with a developmental delay were obese; 21.5% of moms who had a child with autism were obese; and 14% of moms with a typically developing child were obese.
Researchers noted that overweight mothers whose weight approached obese - a BMI of 28 or 29 - had risk levels similar to obese moms.
Mothers with a child with autism or a developmental delay were also more likely to have hypertension during pregnancy, but the association wasn't considered statistically significant. Researchers noted the number of women with high blood pressure in the study was small.
Pregnancy month by month
The U.S. National Institute of Neurological Disorders and Stroke has more on autism.
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