During the early stages of pregnancy, it is recommended that you begin to become accustomed to sleeping on one of your sides as opposed to the back or stomach. Sleeping with knees bent and on the side is probably the best position for comfort as you pregnancy goes on. This sleep position also reduces strain on the heart by shifting your baby’s weight off of the inferior vena cava (large primary vein) which is working to move the blood between the lower extremities and the heart.
Many doctors recommend specifically left side sleeping during pregnancy because the liver is located on your right. By left side sleeping, you keep the baby’s weight off of the liver. Circulation and uterine blood flow are improved by left side sleeping. The opinions of doctors may vary, but most agree that sleeping on either of the sides relieves pressure on the back and is better for the health of baby and mother.
All doctors agree that sleeping on the back should just not be done while pregnant, particularly in later months. While sleeping on the back, the increased weight of the uterus rests on your spine, internal organs, blood vessels and the spine. Conditions such as hemorrhoids, impaired circulation, aches, pains and general discomfort can result from sleeping on the back while pregnant.
Dizziness due to decreased blood pressure is another side effect of back sleeping. In some cases, it can cause an increase in blood pressure. Snoring and sleep apnea can also result from back sleeping as the pregnancy continues.
Shifting positions while sleeping is natural and you are not going to irreparably harm your baby or yourself by accidently rolling on your back at night. It is not likely that your body will naturally shift to cause you to back-sleep when you are in your third trimester. It is too uncomfortable.
The pressure of the baby on the inferior vena cava is uncomfortable enough to awaken you. If this seems to happen often while you sleep, discuss it with your physician. You might want to prop a pillow behind your back to prevent turning over.
Experiment with one or more pillows to find a comfortable position of sleeping for you. Most women feel better with a pillow between the knees or under the belly. A pillow at the lower back often relieves pressure. There are pregnancy pillows available specifically designed in a few different styles to offer comfort and relief. You may want to discuss the best style for your purposes with your physician.