I learned the hard way last year when I made quilts for twins with flannel. I washed after they were completed and one shrunk about 3 inches smaller than the other. It was kind of embarrassing but I gave them anyway and just laughed it off by telling the mom that the littlest quilt was for the tiny one. (there was almost a 3 lb difference in birth weight!). It was weird because the fabrics were the same just alternated colored polka dots (dark blue dots on light background on one and light blue dots on dark background on the other). I pre-wash now.