Baby' Heartbeat

Hi mummies to be, just curious to know..once we check with gyane on baby's heartbeat, and everything is fine...then our next appt will be 2 weeks means how do we know how is the baby doing inside the womb till the next appt? I had an experience where at 6 wks baby' s heartbeat was heard thereafter 3 weeks later suddnly no heartbeat...so just curious if we hev to wait so long for the next appt how do we knoe wats the baby doing inside? Pls share ...