I thought I was finding baby around the same rate around the same stage as got my Doppler when I was 9 weeks. I later discovered it wasn't though and was a bit harder to find the actual heartbeat. I would recommend watching some YouTube videos for tips, once you find the heartbeat the sound is unmistakable, like a fast train or galloping horses. Once I found the heartbeat it's been in the 170-180 range but I can still find whatever it is that comes up at 140-150 too. I think the heartbeat is usually higher than that early on. I also found it helped to have the volume turned up full even though the feedback can be annoying, sometimes I can hear the heartbeat but it's not actually registering on the screen all the time.