Healthcare professionals often recommend the so called "SOS" position. SOS stands for "sleep on your side", and it is the position that is the least uncomfortable for a lot of expectant mothers. Lying on your tummy is obviously out when it is protruding so much from the rest of your body, and back lying encourages heartburn and is not optimal for your blood supply. Sleeping on your left side actually increase the amount of blood and with that, nutrients that get to your baby through the placenta. With the help of a full body maternity pillow or simply some extra blankets or pillows, it will likely be a great position to sleep in for you too. In conclusion, you don't have to lie on your side during pregnancy, but will probably end up doing so. Also take a look at will sleeping on my back hurt the baby?
Have you heard recommendations to sleep on your left side during pregnancy? If so, you are probably wondering why you "have to" lie on your left side when you are expecting, what is so good about it, and if sleeping in other positions is dangerous. To answer that in a few lines, sleeping on your left side does have some special benefits, but the main reason is that it is the most comfortable position for most pregnant women. Sleeping in other positions is not dangerous, and your comfort is the most important. As your belly expands and you develop a true baby bump, you will probably find that sleep becomes a bit more tricky. You might well need more sleep, but find it more difficult to get good quality shut-eye for many reasons. Frequent urination, heartburn during the night, back pain, heavy fetal movement... these are all possible reasons to have a love-hate relationship with sleep. But it is the new shape of your body that prevents you from settling into a comfortable sleeping position.