Children are more likely to develop autism if their mothers were diagnosed with gestational diabetes early in pregnancy, a new study shows.

Women who receive a new diagnosis of gestational diabetes by the 26th week of pregnancy were 42% more likely to have a child diagnosed later with autism, according to the study of more than 322,000 children born between 1995 and 2009.

Thomas A. Buchanan, MD, vice dean for research and chief of the Division of Endocrinology and Diabetes in the Department of Medicine at the Keck School of Medicine of USC, coauthored the study, which was conducted at Kaiser Permanente and was published in the Journal of the American Medical Association.

Overall, about 1 percent of the children in the study were diagnosed with autism by a median age of 5½. Researchers found no increase in autism risk if mothers were diagnosed with gestational diabetes after 26 weeks of pregnancy

Buchanan said this study is part of the field-leading work being done by the Gestational Diabetes Study Group, which is a collaboration of Keck Medicine of USC and Kaiser Permanent Southern California. The Study Group uses a variety of approaches to investigate why gestational diabetes occurs, how and why it turns into diabetes after pregnancy, and what it does to children who are exposed to diabetes in utero.

“We then use that information to develop better approaches to treat or prevent the complications of gestational diabetes,” Buchanan explained. “In the past we have developed more efficient ways to treat gestational diabetes during pregnancy and to prevent diabetes after pregnancy in mothers who have had gestational diabetes.”

The new study found no increased risk of autism if women had type 2 diabetes before becoming pregnant, possibly because these women already had their blood sugar under control.

Anny Xiang, MD, of the Kaiser Permanente Southern California Department of Research and Evaluation said the study does not reveal why developing diabetes in pregnancy increases the risk of autism. It’s possible that high blood sugar levels have long-lasting effects on a fetus’ organ development and function, said Xiang, the study’s lead author.

Buchanan said that many of the current recommendations for clinical care of mothers during and after pregnancy are the result of work that has been done by the Gestational Diabetes Study Group, of which he and Xiang are founding members.

In recent years, the group has developed a strong focus on what exposure to diabetes in utero does to children, he said.

“We know that they tend to be more obese and at higher risk for diabetes than other children,” Buchanan said. “Dr. Katie Page at USC is studying why that occurs.”

It has been known for a while that exposure in utero to severe maternal diabetes can case major brain malformations in fetuses. Buchanan said the new information suggests that exposure to relatively mild maternal diabetes, as in gestational diabetes, can also cause more subtle brain abnormalities that become manifest as autism spectrum disorders, or ASD.

Buchanan noted that both gestational diabetes and ASD have been on the rise in the past decade, so the new study suggests a possible link to help explain why.

“We don’t know yet whether earlier diagnosis and treatment of gestational diabetes can reduce the risk of ASD in offspring, but treatment can reduce the risk of other complications,” Buchanan said. “The study provides an important rationale for diagnosing and treating this type of diabetes as early as possible during pregnancy.”

— Les Dunseith