Edit to my earlier post:
I'm seeing 2 different things proposed on here. If you are concerned with crinkling, then you want a poly batt (or at least a blend -- like Warm & Natural) & poly thread, with far apart quilting. The more densely you quilt & the more curvy your lines, the more it will crinkle. Crinkling is a property of all cotton fabrics. It's just a fancy name for wrinkling & does not involve the fabric actually shrinking. You can get rid of this effect by either wet blocking or steam blocking your quilt after laundering it.
Then, there is the actual shrinkage rate of cottons. Lower quality cottons (including lower quality muslins) shrink more. The "dressmakers'" muslin they sell at JAF for dirt cheap shrinks quite a lot. If it's a wall quilt, you could back the whole top with stabilizer so it doesn't shrink. For a bed quilt, your best bet is to pick a high loft batting (either Warm & Plush, or a high-loft poly batt) and quilt it more densely. With quilting lines closer together, it is very important to increase the loft of your batting, or else the quilt will end up feeling like a floor mat.
In the future... if I'm ever trying to make something from cheap muslin that's going to be washed (which is incredibly rare), I would pre-wash it in hot water & dry it on high heat. Designer muslin usually doesn't shrink noticeably more than other designer cottons -- at least not how I launder, which is cold water & low heat.