I never prewash but I always wash the quilt before I give it away. When I wash it I use a sheet of Shout Color Catcher in the machine and I've never had a problem yet. I like the look a quilt takes on after washing and if there is a "hole" in the quilt that I somehow missed it will show up after being washed. 98% of the time I use Warm and Natural batting so the shrinkage from the fabric top and bottom and the batting is about the same.