Low fetal heartbeat..mc #2?

Jenny • Late 20's. TTC #1 Recovering from 2nd miscarriage at 6-7 weeks.
Feeling pretty low. Went in for a 6 week 4 day ultrasound on Friday. They found two sacs - one was empty, the second had an embryo measuring 6 weeks 1 days with a heartbeat of 84. They gave us 50/50 odds. But I'm already preparing for worst as my pregnant symptoms are minimal.
We had a miscarriage at 6 weeks almost exactly a year ago. We got pregnant this time after <a href="https://glowing.com/glow-fertility-program">IUI</a> #1 after TTC 1 1/2 years. We were really excited for this one...heartbroken and hoping for a miracle at a follow up ultrasound next Wednesday. We're both 29, healthy and trying for our first. 
Thanks for listening. 
Jen