At 10 weeks of pregnancy it can be really impossible to hear a babies heartbeat with just a stethoscope.
Before 20 weeks of pregnancy the only good way of hearing a babies heartbeat is through use of a heart rate doppler that the doctor can use to hear the babies heartbeat before 20 weeks of pregnancy.
During 20 weeks of pregnancy then you can usually hear the babies heartbeat using a stethoscope.
However sometimes you may not be able to hear the babies heartbeat using a doppler before 12 weeks of pregnancy which is also normal and sometimes it just takes a bit longer to be able to hear your babies heartbeat even using the heart rate doppler.
But like I said by 20 weeks you should be able to easily hear the babies heartbeat with a standard stethoscope.