A newly released study of the possible links between a mother's condition during pregnancy and the chance her baby will suffer a developmental disorder comes to a provocative conclusion: obese moms may have a greater chance of delivering a baby with autism.

The population-based study conducted between January 2003 and June 2010 found that women who were obese during pregnancy were approximately 67 per cent more likely to have a child with autism spectrum disorder.

Researchers studied approximately 1,000 California children between the ages of two and five, more than two-thirds of whom had been diagnosed with autism or developmental delays.

Compared with the average woman who has a 1 in 88 chance of having a child with autism, factoring in obesity increases those odds to 1 in 53, the study's authors found.

The research stops short of proving a causal link between obesity and autism, but its authors note the growing prevalence of obesity in the American population means the mere possibility should be cause for concern.

The mothers' conditions during pregnancy were self-reported, with medical records confirming the claims of more than half the women. There was no information on the mothers' blood tests during pregnancy, nor their diets or other habits in those months.

The researchers say there were no other factors, however -- such as discrepancies in education, race, ethnicity or health insurance -- that could influence the results.

The study, which was partially funded by the U.S. National Institutes of Health, was published Monday on the website of the journal Pediatrics.

"If you are planning a pregnancy you might want to think about losing weight, getting your exercise routine in order and controlling your blood sugar," said Irva Hertz-Picciotto, an autism researcher at the University of California.

Researcher Tom Frazier of the Cleveland Clinic's Center on Autism said the latest study should be seen as a warning about the general risks of unhealthy pregnancies.

"For a mother who is pregnant, she is going to pay very careful attention to their blood pressure...and to whether or not they're overweight and to a make sure that any diabetes is under control," he told CTV News.

A recent report released by the Centers for Disease Control and Prevention in Atlanta estimated that one in 88 American eight-year-olds have autism -- the disorder often characterized by repetitive behaviours and difficulties in social interaction as well as verbal and non-verbal communication. That was up from about one in 110 back in 2006, and one in 150 in 2002.

In Canada, a report from the National Epidemiologic Database for the Study of Autism noted that autism diagnoses were up in Prince Edward Island, Newfoundland and Labrador and southeastern Ontario too, with increases since 2003 ranging from 39 to 204 per cent, depending on the region and age group.

Those numbers, which some experts note may be rising due to increased awareness and diagnostic improvements, have been growing alongside obesity rates.

In the U.S., more than one-third of pregnancy-age women are obese. According to the World Health Organization, someone whose Body Mass Index (weight(kg)/height(m)2) is greater than or equal to 30 is considered obese. While the formula does not apply to pregnant women, their recommended weight gain during pregnancy is also based on BMI.

Based on its figures from 2008, the WHO estimated there were 1.5 billion overweight adults worldwide, including nearly 300 million obese women.

Other studies have linked obesity during pregnancy with increased risks of stillbirths, preterm births and birth defects.

Scientists trying to pin down the cause of autism have previously examined genetics as well as the effects of illness and use of medication during pregnancy. Antiobiotics have also come under fire, due to the belief their over-use could alter bacteria found in human digestive systems. Other environmental factors have even been scrutinized, including the use of certain chemicals and pesticides.

Suzanne Lanthier, who has an autistic son, said she welcomes any new knowledge about a condition that affects about 190,000 Canadians.

"My son is now 13 and when he was first diagnosed, we could fill the amount of research that was going on onto a couple of pages," she said.

With a report from CTV's Scott Laurie