I heard the heartbeat early, like about 8 weeks when I went for a dating scan (that was with ultrasound though not doppler). I would think by now they could hear it with a doppler - maybe just ask them at the next one to try for you just for your peace of mind... sometimes i think care providers forget how each of these little milestones means so much to us so they dismiss things as unnecessary that would make us feel a lot better or that we would find special - so it pays to ask!