U/S dont detect heartbeat. Restoring.

My Wife's outer ultrasound (External) didnot detect heartbeat today whereas a week back the internal ultrasound detected a perfect heart rate. She was 8 week 4 day pregnent that day and as per today's ultrasound (done after 7 days) the fetus age is shown as 8 week 6 days. We have read over internet and heard that sometime the ultrasound do not detect heartbeat and we should wait for some time.. She had spoting, clotting and bleeding problem starting from 8th december and thats why we had gone for ultrasound on 12th Dec. Today she is not having any bleeding or any cramp she still have the pregnancy signes... I want to ask experts, what to do...can we wait and go again for ultrasound and what are the chances of heartbeat restoring.