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The blood sugar disorder, known as gestational diabetes, was linked to a moderately increased risk for an autism spectrum disorder in a study of more than 320,000 U.S. children, said study researcher Anny Xiang, director of statistical research at Kaiser Permanente Southern California.
However, it was an "observational study" and cannot prove a direct cause-and-effect relationship between gestational diabetes -- which affects up to 9 percent of pregnant women in the United States -- and autism.
"To provide perspective, this increased risk [of autism] seen with early gestational diabetes translated to around seven additional cases per 1,000 pregnancies over that seen with pregnancies that didn't involve [gestational] diabetes," Xiang said.
No increased risk of autism was associated with type 2 diabetes diagnosed before pregnancy, the study found.
One expert urged caution in interpreting the findings.
"Although this study suggests that development of gestational diabetes during the first or second trimester of pregnancy puts a fetus at increased risk for an autism spectrum disorder, the magnitude of this risk -- if real -- is relatively small," said Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at the Cohen Children's Medical Center of New York in New Hyde Park, N.Y.
"Although researchers are eager to identify as many risk factors for autism as possible, the reality is that many different health exposures and risk factors have been linked to autism spectrum disorders," said Adesman, who was not involved in the study.
Previous studies have produced mixed findings about whether gestational diabetes increases the risk of the developmental disorder in offspring, Xiang said.
About one in 68 U.S. children has an autism spectrum disorder, according to the U.S. Centers for Disease Control and Prevention. These children commonly have trouble with social interaction and communication.
For the study, published April 14 in the Journal of the American Medical Association, Xiang's team followed more than 320,000 children born from 1995 through 2009 at Kaiser hospitals in Southern California. During roughly 5.5 years of follow-up, 3,388 children were diagnosed with autism.
The researchers determined that babies exposed to gestational diabetes by the 26th week of pregnancy had a 42 percent increased risk of developing some degree of autism compared with children not exposed to gestational diabetes. The finding held even after taking into account other factors that could affect risk, such as maternal age, education and weight, they said.
Xiang speculated that the link was seen for gestational diabetes and not previously diagnosed type 2 diabetes because the mothers with type 2 diabetes may have had their blood sugar under better control.
Xiang cannot explain the mechanism behind the link with certainty. However, she said that the high blood sugar levels involved in gestational diabetes could interrupt normal brain development at a crucial time period.
Mothers-to-be should get their blood sugar checked early in pregnancy, Xiang said.
Under guidelines from the American College of Obstetricians and Gynecologists, women are screened for gestational diabetes, usually at 24 to 28 weeks. A woman who has risk factors for gestational diabetes -- such as being overweight, older than 25 or having a history of gestational diabetes -- should consider earlier screening, such as at the first prenatal visit, Xiang said.
The researchers said early screening for autism in children born to mothers with gestational diabetes may also be warranted.
But Adesman isn't so sure about that.
"I think this recommendation, though well-intentioned, may be a little premature," he said. "On the other hand, parents should always share with their child's pediatrician any concerns they have about their child's development."
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SOURCES: Anny Xiang, Ph.D., senior research scientist and director, statistical research, Kaiser Permanente Southern California, Pasadena, Calif.; Andrew Adesman, M.D., chief, developmental and behavioral pediatrics, Steven & Alexandra Cohen Children's Medical Center of New York, New Hyde Park, N.Y.; April 14, 2015, Journal of the American Medical Association