Depending on your birthing position, you won't be able to see anything anyway - even without a sheet. Both times, I gave birth laying on the bed and I saw nothing at all until my baby was born and brought up onto my chest. Seriously, you'll be so preoccupied with your contractions and pushing that you won't even notice what's happening down the business end of things. You may even find a sheet gets in the way and annoys you. Good luck!