sleeping on the left side is the best comfortable position to sleep for a pregnant womanThe status of restful sleep for a pregnant woman is one of the most prominent problems that caused her insomnia and fatigue with entering the fifth month of pregnancy because of the increased size of the stomach day after day. This is because the liver is in the right side and therefore sleeping on the left side decrease the pressure on the liver by the uterus,also this situation Help the kidney to make it's function so reduces the swelling of the feet and hands, but sleep on the left side also helps to increase blood flow to the placenta. N.B:sleeping on the back is one of the positions that must be abandoned because the large size of the fetus causing pressure on the back and the inferior vena cava, which carries blood from the lower part of the body to the heart, also causes pressure on the intestines, which slows down the digestion process. Also, sleeping on your back during the last months of pregnancy increases the chance of back pain and decrease in blood pressure . Source :Medical Inspiration: Best sleeping position during pregnancy