I don't prewash unless it is very stiff or flannel. I wash all my quilts in cold water and very mild low sudsing soap. I honestly never have had a shrinking problem. The colors also stay much brighter without the hot water and detergents. :D
I do have quite a stack of fabric and the chemical smell is offensive if the room is closed up for long periods.
Ido swear to this on my great grandmothers gold tooth. :twisted: