What would cause a a twitching/fluttering feeling between sternum and stomach area right in the center of the abdomen?

Only 100 items or so: "How does my bosom twitch? Let me Count the Ways!" And then, quick, camera cuts to the Tootsie Roll Owl- "1, 2, THRRRREEEE!"....Well, in your case twitching/fluttering in the chest could be something as simple as twitching of the muscles. Nothing more to say about that...comes, goes, NEXT! Or it could be due to stress/anxiety, or something more sinister such as a heart rhythm issue. See your doc.