Early in the pregnancy, sleeping on your back is safe. In the third trimester (starting around 28 weeks), it is not recommended that you lie flat on your back for a prolonged period of time because the weight of your uterus presses on the major vein in your back. When you are sleeping, it is hard to control your position. If you wake up on your back, you probably awakened because your body was telling you to shift position. Some women wake up feeling dizzy, short of breath, or with heart palpitations. These symptoms should resolve quickly if you shift to either side. As your pregnancy progresses, try to sleep on one side or the other, or use a cushion to ensure that you are not completely flat on your back to avoid nighttime awakenings and ensure proper blood flow to your baby.
There is no problem with sleeping on your stomach in early pregnancy, as the uterus is protected by your pubic bone. As the pregnancy progresses, sleeping on your stomach will become uncomfortable, which is the cue to stop.
Some prescription sleep aids can be used in pregnancy but should be discussed with your OB provider before starting. These medications can be habit forming, and in general, are used sparingly in pregnancy. There are over-the-counter sleep aids that are safe to use during pregnancy and are not habit forming, including Benadryl, Tylenol PM, and Unisom. These medications should be taken according to the directions on the package.
Electric blankets are safe to use in pregnancy as long as the temperature setting is not too high. In general, this means high enough to keep you warm, but not so high as to burn you or elevate your temperature. If you are concerned, you can take your temperature to make sure it is in normal range, under 100 degrees.