Researchers strongly stress, however, that it is not the weight gain itself that is being considered a cause of autism. Nor do the current findings show in any way how pre-pregnancy weight affects future children.
Lead author Dr. Deborah Bilder emphasized that when it comes to autism risk, weight gain during pregnancy should not be seen as the culprit but rather the canary in the coal mine. She warned against making any dietary changes based on these findings.
Instead, the team believes that a slightly higher increase in weight during pregnancy might be an indication that a more complex process — possibly involving hormone and inflammation problems — is occurring, and that weight gain is just a reflection of this.
Weight gain during pregnancy might serve as an easily recognizable marker for a constellation of events that collectively increase the risk for autism.
“Although weight gain during pregnancy was associated with autism risk, the modest difference in weight gain found suggests that weight gain serves as a marker rather than a cause for autism,” said Bilder, a pediatrician and assistant professor in the department of psychiatry at the University of Utah, in Salt Lake City.
“As a marker, it would share an underlying cause with autism, such as hormone imbalance or inflammation,” she added.
The authors noted that autism is no longer considered a rare disorder, with some estimates showing that autism affects about one in 88 children in the United States.
For the study, the researchers focused on two groups of children with autism in Utah. Maternal weight-gain patterns during pregnancy were analyzed in both groups.
The first group included 128 children whose results were compared to nearly 11,000 mothers of healthy children of a similar age and gender. The second group included 288 children whose results were compared to maternal weight gains leading up to the birth of each autistic child’s healthy siblings.
During pregnancy, small increases in weight (in 5-pound increments) were linked to a slightly higher but significant risk for autism among the offspring. On the other hand, body-mass index (a measurement of body fat based on height and weight) at the start of pregnancy was not linked with a higher risk for autism.
The findings showed an average difference of only about 3 pounds in weight gain when comparing mothers of children with and without autism.
“Good nutrition is essential to a healthy pregnancy,” Bilder said. “Clear guidelines are in place that pregnant women can discuss with their medical providers regarding the recommended weight gain for a healthy pregnancy.
“This study was not designed to impact these guidelines, but rather to provide future direction to researchers as we investigate possible causes that link risk factors with autism.”