Odd heartbeat using doppler

Hi.

I have been on here before and hoped that I'd never have to ask questions in this category again, but here we go ...

I posted here last November, when my girlfriends ultrasound scan showed a sac but no baby. It turned out in the end that she had a silent miscarriage and it left us devastated.

It's taken a while but we found out around a month ago that she was pregnant again.

She has her first ultrasound scan next week (12 weeks, apparently) but we could wait that long so bought a Doppler off the Internet (one that had a good review rating) and tried to use it today.

It took us ages to find anything, but then we found a beat but it only measured 60 beats per minute.

We thought that this could just be hear heartbeat, but we couldn't pick up that same beat anywhere else in the area.

We couldn't pick up another beat anywhere else apart from that one, and around her heart.

Is this just her heart beat and there's no baby (again), or are we missing a beat?

We can sometimes hear a galloping noise with it, but that's not constant and could just be our mind playing tricks with us.

Please provide some support/advice.