Twins! One with slow heart rate :-/

Erica • Second pregnancy first viable!!! Unplanned but we're both really excited! Any advice or encouragement is appreciated!🙏
Went to the hospital yesterday as I was spotting.... And am having a high risk pregnacy (I conceived with my IUD and had it removed during week 5)  I'm at 7 weeks 6 days and have just found out that there are two heartbeats! But both are low and one is quite low. I will have a U.S. in a few days to see how they are doing for certan.... But the fetal heart rate chart with correlation to risk of miscarriage is really discouraging. I was also told there was nothing to be done, but hope that my hCG doesn't drop as well....
My hCG is quite high which they told me was incouraging. But one FHR is at 87 and one is really low 39.... 
The chart says that below 70 is a 100% chance of miscarriage while 80-90 is 79% chance. 
Has anyone had a low fetal heart rate for it to then become stronger? Then carried to term? 
Obviously (considering I had an IUD) this was unplanned but me and my partner are really excited and this wouldn't be our first loss... 
Any encouragement? Or is there really nothing I can do?