Researchers from UC Davis determined that California babies conceived in March had a significantly higher rate of autism, perhaps adding to a body of research that links spring and summer pesticide exposure to birth defects.
The report, which was published in the journal Epidemiology, found that children conceived in March have a 16 percent greater chance of being diagnosed with autism than children conceived in July. Researchers reviewed birth records for 7 million children born in California between 1990 and 2002.
The findings are a "starting point for further inquiry" into whether there is a connection between the increased autism incidence and additional exposure to pesticides that comes with spring and early summer planting, the report says. If such a connection is made, it would align with other studies showing that babies conceived in the spring have a higher rate of birth defects, such as Down syndrome and spina bifida.
Other research has found ties between [PDF] occupational pesticide exposure among farm workers and birth defects. In one high-profile case, three babies born within three weeks of each other in February 2005 all had similar birth defects. Their mothers worked for the same tomato grower and were exposed to similar chemicals. Researchers could not determine that the pesticides clearly caused the birth defects, but called the incident a "cause for concern."
Researchers delved into a rash of birth defects identified in rural Kettleman City, a California town surrounded by agriculture fields, but were not able to pinpoint a cause.
A study released last year showed that pesticides, likely from residue on food, were linked to attention deficit and hyperactivity disorder in children who were 8 to 15 years old. That study found that kids with higher-than-average levels of pesticide metabolites in their urine were also nearly twice as likely to have ADHD.
The California Department of Public Health has also studied the issue and found that certain types of birth defects [PDF] are associated with women who said they were exposed to household gardening pesticides and those who lived within a quarter-mile of agricultural fields.
Researchers have repeatedly concluded that more research is needed to better understand how planting season and pesticides relate to birth defects.