A common misconception is that you can't do ANY core work during pregnancy - this is SO FAR from the truth. And, in fact, doing core work is very beneficial!
Perform each exercise for 30-45 seconds, on each side as applicable, for 3-5 rounds.
Elevated Plank with Reach
Elevated Plank with Shoulder Touch
Side Plank Raise
Single Leg Extension
Let me know how this core workout felt!