Basically, pregnancy pillows are specially designed to fit on certain parts of your body and add support. There are several different types made to fit on your lower back, between your knees or thighs, on your neck, or on your stomach.
As you progress through the stages of pregnancy, it will be more and more difficult to get comfortable. It will likely get to the point that you have a hard time sleeping because every way you lay causes discomfort. As your stomach gets bigger, sleeping on your back will make you feel as though you can not breathe, and, of course, sleeping on your stomach does not work. For these reasons, you will most likely end up on your side. However, the extra weight makes your hips hurt and you are not able to reposition very well. Luckily, pregnancy pillows provide relief!
The ideal position is lying on your side with a pregnancy pillow between your knees/thighs and another behind your back. The pillow between your legs offers support and relieves some of the pressure on your hips, while the pillow behind your back allows you to lie back slightly when you want to reposition. This gives you a range of motion and also gives your back a break. This way, you have the option to lie at almost any angle on each side, instead of being restricted.
Sitting for long periods of time also makes your joints ache when you are pregnant. A pregnancy pillow behind the back will also help this, as well as propping the feet up periodically. Some women feel relief from placing a pillow in their laps to support the extra weight of their stomachs. These techniques can also be used when driving to prevent stiffness and discomfort.
There are many models of pregnancy pillows available. Some are made of regular pillow materials, such as cotton or down, and other, more expensive models, are made of memory foam. Take your time and try out the different kinds to pick the most comfortable for you.