While diagnoses of autism spectrum disorder have increased in recent years, the factors behind this rise remain relatively mysterious and even controversial. However, a growing line of research suggests that many of the risk factors for the condition emerge long before birth. Now, a major study from Johns Hopkins University has found that maternal obesity and diabetes “substantially” increase the risk of autism in children, offering compelling new evidence that the disorder may begin during pregnancy or even earlier.
The study, published in the journal Pediatrics, found that children born to obese women with diabetes were four times more likely to develop autism than those born to women of a healthy weight without diabetes. Individually, maternal obesity or diabetes was linked to twice the odds of giving birth to a child with autism compared to mothers of normal weight without diabetes, but the combination of the two conditions compounded the risk, the study showed.
“We have long known that obesity and diabetes aren’t good for mothers’ own health,” said study leader Xiaobin Wang, MD, ScD, MPH, Professor in Child Health at Johns Hopkins Bloomberg School of Public Health and director of the Center on the Early Life Origins of Disease. “Now we have further evidence that these conditions also impact the long-term neural development of their children.”
Autism, or autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by significant social, communication and behavioral challenges, though the range and severity of symptoms can vary widely. According to data compiled by the Centers for Disease Control and Prevention (CDC), the number of children diagnosed with the condition has risen greatly over the past fifteen years: in 2000, around 1 in 150 children were diagnosed with ASD, compared to 1 in 68 children today.
Experts are unsure as to whether this increase is due to an actual rise in the prevalence of autism or merely improved methods of diagnosis. For example, one recent study found that that much of the increase in U.S. autism diagnoses over the first decade of this century could be the result of diagnostic reclassification.
At the same time, researchers have also discovered a number of risk factors that could account for at least some of the increase in autism diagnoses, including parallel changes in maternal health and exposure to environmental risks. In 2011, a meta-analysis of forty studies assessed the association between perinatal and neonatal factors and ASD risk, concluding that there was “some evidence to suggest that exposure to a broad class of conditions reflecting general compromises to perinatal and neonatal health may increase the risk.”
Among those risk factors are obesity and diabetes, both of which have risen to epidemic levels among reproductive age women over the same period that autism diagnoses have spiked. Though previous research has looked at the roles of maternal obesity and diabetes on autism risk, this new study is the first to examine both the independent and combined effects of the two.
The study followed almost 3,000 children who visited the Boston Medical Center between 1998 and 2014. It used electronic health records to track whether these children were diagnosed with autism, along with factors like the mother’s pre-pregnancy weight and whether she had been diagnosed with diabetes before or during her pregnancy.
‘The risk for autism begins in utero’
Almost 4 percent (102) of the 3,000 children were diagnosed on the autism spectrum over the six-year study period. About 5 percent (137) were diagnosed with some form of intellectual disability, and nearly one-third (864) were diagnosed with another developmental disability. Some were diagnosed with more than one condition.
Besides quadrupling autism risk, the combination of maternal obesity and diabetes was also linked to a similarly higher risk for giving birth to a child with an intellectual disability, the investigators found. However, most of the increased risk for intellectual disability was seen among babies who were simultaneously diagnosed with autism.
Along with pre-pregnancy diabetes, gestational diabetes — a form that develops during pregnancy — was also linked to a higher risk of an autism diagnosis, mirroring the findings of another study published earlier this year.
“Our research highlights that the risk for autism begins in utero,” said co-author M. Daniele Fallin, PhD, chair of the Bloomberg School’s Department of Mental Health and director of the Wendy Klag Center for Autism and Developmental Disabilities. “It’s important for us to now try to figure out what is it about the combination of obesity and diabetes that is potentially contributing to sub-optimal fetal health.”
While the mechanisms linking a mother’s obesity and diabetes to a child’s risk of autism are not clear, some research has suggested that obesity and diabetes may disrupt the functioning of a mother’s immune system, and this in turn may contribute to the development of autism in the child, the researchers said.
Both obesity and diabetes may also promote inflammation in a pregnant woman’s body, and intrauterine and fetal brain inflammation have been implicated in the development of autism in children, the study said.
Another possible mechanism relates to folate, a B-vitamin vital for human development and health. Studies indicate that obesity may disrupt the uptake of folate, making it harder for the body to properly use the chemical, the researchers said. In turn, this could contribute to an increased risk of autism in the fetus.
The researchers say that women of reproductive age who are thinking about having children need to not only think about their obesity and diabetes status for their own health, but because of the implications it could have on their children. Currently, more than a third of women of childbearing age are obese, roughly one in 10 have diabetes, and an estimated 2 percent to 10 percent of mothers develop diabetes during pregnancy, the authors note. Better diabetes and weight management — starting before pregnancy — could have lifelong impacts on mother and child, they say.