The forward expansion of your body during pregnancy combined with the softening of connective tissues as your body prepares itself for labor can result in pain in your hips and pelvis. Keeping the deep hip rotators (the muscles underneath the buttocks and around the lower hips) flexible can keep pain at bay.
Sitting hip stretch
Sit in a chair and bring one ankle across the opposite knee. Wanting to tuck your pelvis under at this point is common, especially if your hips are tight. Instead, untuck your pelvis (in other words, stick your butt out) to increase the stretch in this area [shown]. Sitting on a rolled towel will help you move your pelvis forward into the correct position. Switch legs and repeat.