Not a scientific response but I would say you should wash them. Consider their journey through the supply chain and what they came into contact with through the distribution/warehousing process:- Raw material shipped (import/export) to Textile manufacturer who then spin it in their manufacturing sites before sending it on to (import/export), clothing manufactures who then run it through their manufacture equipment before packing and sending onto retail/wholesales.
Personally I will be washing Everything. Maybe I am a paranoid new mum to be, I know. 