Getting and staying comfortable in bed may be one of your greatest challenges during pregnancy, particularly if you're used to sleeping on your stomach or your back. Both positions present problems during pregnancy. During your first trimester, tender breasts may keep you from sleeping on your stomach, and as your belly grows, lying face-down will become increasingly uncomfortable.
Sleeping flat on your back puts the full weight of your uterus on your back, intestines, and your inferior vena cava (the vein that transports blood from your lower body to your heart). Back-sleeping can also increase your risk for backaches and hemorrhoids, inefficient digestion, and impaired breathing and circulation. Lying on your back in the second and third trimester can also cause changes in blood pressure. For some women, it can cause a drop in blood pressure that can make them feel very dizzy; for others, it can cause an unwanted increase in blood pressure.
What you can do about it
During the first half of your pregnancy, it's a good idea to start training yourself to sleep on your left side whenever you can. This position benefits your baby by maximizing the flow of blood and nutrients to the placenta. It also helps your kidneys efficiently eliminate waste products and fluids from your body, which in turn reduces swelling in your ankles, feet, and hands. Sleeping on your right side is fine, too. You'll probably need to alternate between your left and right side to remain comfortable. (If you wake up at night and find yourself on your stomach or back, don't worry you haven't done any harm to your baby. Just roll back onto your side.)
Here's how many pregnant women feel most comfortable in bed: Lie on your left side with your knees bent and put a pillow between your knees. Arrange other pillows under your belly and behind your back for extra comfort and support. You can buy special maternity pillows for this purpose, though you may find that regular pillows work just as well. If you suffer from heartburn or breathlessness, you may also find it helpful to prop your upper body up a bit. In your third trimester, wearing a sleeping bra and a maternity belt can give extra support to your breasts, belly, and back.
A final tip: If lying on your side puts too much pressure on your hips, buy a soft egg-crate foam mattress pad. The egg-carton-shaped layer goes on top of your mattress and under the sheet and regular mattress pad for added comfort and air-circulation and is available in a range of sizes.