Damage fetal cardiac tissue

Hey ladies! I went to my 1st doctor's appt when I was 8 weeks. I was expecting to hear the heart beat for the 1st time, however I was told by the doctor they don't listen to the heart beat in the early stages because it can damage the fetal cardiac tissue. Have anyone heard about this? I can't seem to find any research to support her theory. So I was told I would hear the heartbeat at 12weeks and there after. Wasn't told anything was wrong with the baby either. Was told moving along healthy.