the reason I was given was that the newborn could suffocate - the mattress protector doesn't allow enough air circulation and if the newborn went face down then it couldn't breath.
what a whole lot of crappo! 1. babies cant roll onto their tummies for months. 2. when they can they are more than capable of putting their head to the side. 3. if ur bub wants to tummy sleep, get a breathing moniter (with our without matt protect).