How is a MMC diagnosed?

Korey
I've seen several girls share their stories about missed miscarriages (I was unaware that this was possible before that). I'm not going to have a scan until week 12 (currently at 6+5)....how will my doctor know that my pregnancy is still viable and not a MMC? Blood HCG? Fetal Doppler? The suspense is killing me! Any info would help to put my mind at ease. Thank you!