Pigeon Pose for Pregnancy
With a few pillows, a nice soft mat and a strong foundation as you set up the pose, pigeon can be really really nice during pregnancy.
I recommend doing this same modification in the fourth trimester (in fact, for the first six months post-partum when the relaxin hormone is still in your system).
Here is the tutorial. Please listen to your body and go into (and out of) the pose slowly. Come back from your flexibility edge. Focus your attention on releasing tension in your belly instead of trying to "stretch out your hip". And breathe into the sensations you feel in your body.