Doctor Appointment Question? Heartbeat

Faythe
I just had my first appointment this week, everything was great. Now, my next appointment is in 4 weeks, I'll be 12 weeks along at that point. The doctor said I won't get another ultrasound until 18-20 weeks. My question is, do they still listen for a heartbeat on the appointments in between now and then? 
I just want to make sure everything is ok when I go in. My sister had a miscarriage with no symptoms at all. She didn't know until they did her first ultrasound. 
This is my very first pregnancy, so I'm just not sure.