As your pregnancy progresses and the size of your uterus increases, you may find it harder to get comfortable in bed. Early on in pregnancy, you can sleep on your stomach. Eventually, that position can become uncomfortable. But it's OK to sleep on your stomach if it is comfortable. Lying on your back is not recommended because of pressure on the inferior vena cava. That is a major vein that returns blood from the lower body to the heart. The increased pressure on the back and intestines can also cause discomfort.
The best sleeping position during pregnancy is on your side. The left side is especially good because it lets the most blood flow to the fetus. It also improves your kidney function. One choice is to place a pillow between your knees and one under your abdomen. This can create enough of a tilt to help you sleep more comfortably on your side. You might also find it helpful to put a pillow behind your back for extra support. Talk with your healthcare provider if you have any questions or concerns about sleeping positions during your pregnancy.