12 week scan but didn't hear the heartbeat?

I thought I would've heard my baby's heartbeat at my scan yesterday but didn't, I see lots of people posting how many beats per minute etc yet they didn't say anything like that to me, loved seeing it on the screen and I do have a Doppler at home so I get to listen to it, but it would've been nice to see and hear it too. Any one know why this is? I'm from England