Pesticides in pregnancy and autism: an early finding

A study in California found that mothers of children with autism were twice as likely as mothers of typically developing children to have used pet shampoos containing pyrethrins (a flea and tick treatment) around the time of pregnancy.

The results were presented by Irva Hertz-Picciotto, PhD, at the 7th Annual International Meeting for Autism Research. Participants in the Childhood Autism Risks from Genetics and the Environment (CHARGE) study were asked about pesticide use during pregnancy and around birth. Products containing pyrethrins (pet shampoos and some sprays for flies, ants and cockroaches) were linked with a higher risk of autism.

Dr Hertz-Picciotto stressed that these are preliminary data that need to be checked in other studies, and that autism has many causes, with many genetic as well as environmental factors involved.

The researchers looked at 333 children aged 2 to 5 with autism and 198 typically developing children, all long-term residents of California. Autism was diagnosed with the Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview (ADI). In a 90 to 100-minute telephone interview, mothers were asked what they used to control insects (sprays, ant poison, pet shampoos, weed killers) from three months before pregnancy until the child was one year old. No link was found with pesticides that didn't contain pyrethrins.

An earlier study by Eric Roberts, MD, of the California public health department found that pregnant women living near fields sprayed with organochlorine pesticides had a higher risk of having a child with autism.

Pyrethrins replaced organophosphates as flea treatments about twenty years ago. They act on the nervous system and sodium channels of insects, killing them, and there is concern that they might cross the blood–brain barrier while the baby's brain is developing. Pyrethrins break down quickly outdoors but last longer indoors, for example on pets' fur, so exposure can continue. Until more is known, it is sensible for pregnant women to limit their contact with household pesticides and to follow product safety instructions.