Gestational diabetes increases autism risk

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

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

Overall, about 1% of all children in the study were diagnosed with autism by a median age of age 5½. Having gestational diabetes, the kind diagnosed during pregnancy, increased the chance of having a child with autism to 1.4%.

Researchers found no increase in autism risk if mothers were diagnosed with diabetes after 26 weeks of pregnancy. A typical pregnancy lasts 40 weeks.

Authors also 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, according to the study, published in the Journal of the American Medical Association.

Diabetes interferes with the body's ability to move the sugar provided by food into cells. That can lead the levels of sugar in the blood to rise to unhealthy levels, damaging blood vessels.

Anny Xiang of the Kaiser Permanente Southern California Department of Research & Evaluation says the study doesn't 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, says Xiang, the study's lead author.

Gestational diabetes increases a number of risks for a fetus, including death, says Susan Levy, an associate professor of pediatrics at Center for Autism Research at Children's Hospital of Philadelphia, who was not involved with the study.

The new study adds to a growing body of research that suggests the brain changes related to autism occur long before delivery, says pediatrician Paul Wang, head of medical research at Autism Speaks, an advocacy organization, who was not involved in the new study. He notes that brain scans can now detect differences between autistic children and other kids when they're only a few months old.

Several studies have found an increased risk of autism in the children of mothers who develop the flu or other infections during pregnancy.

Pregnant women also are more likely to have children with autism if they don't get enough folic acid, if they're exposed to pollution or if they take the anti-seizure drug valproic acid, research shows.

Other studies have found an increased risk of autism in children who were born prematurely or very small, or who were born less than one year after an older sibling. Older mothers and older fathers are also at higher risk of having children with autism.

Genetics plays a major role too, Wang says. About 15% to 20% of people with autism have a known genetic mutation that causes the condition. If one child in a family has autism, subsequent children have about a 20% chance of also having autism, Wang says.

Numerous studies have debunked the myth that autism is caused by vaccines.

"Autism appears to arise very, very early in brain development," Wang says. Still, he notes, "The vast majority of women with diabetes do not have children with autism."

Wang notes that good prenatal health care reduces the risk of a wide variety of health conditions in infants.

"If you are pregnant or thinking of becoming pregnant," he says, "make sure to get appropriate medical care."