The risk of autism is absolutely nil. The current consensus is that autism begins in the brain shortly after conception. Genetics appear to be the determining factor, but the exact mechanism is poorly understood and the precise gene combinations have yet to be identified.
Andrew Wakefield's MMR-autism study has been confirmed to be fraudulent, with no other researchers being able to confirm his findings. Because Wakefield published his "research" outside of the peer review process, and the damage done to public health, he is no longer permitted to practice medicine in the U.K.
On top of that, nothing that you can see or touch is "chemical free". Everything on planet Earth is made exclusively of 98 chemical elements combined in millions of different ways to yield substances with different chemical properties.