Instructables user kinawera modified an old pillow she had to make a pregnancy pillow. I didn’t know what this was until I read the tutorial, but it makes sense: a pillow to support your belly while you sleep on your side, held in place by being wedged under your body. She writes:

As your belly grows larger and straight outwards, this can make sleeping tricky, because lying on your side becomes uncomfortable. Your lump wants support. Here’s a quick and easy pillow that will get you through the mid-to-holy crap stages of largeness. This looks pretty crude but it is study, and really works. You could make it neater and tidier but most pregnant women have other things to do, like putting baby latches on the plutonium cabinet.