Miscarriage at 8.5 Weeks: Understanding Risk Factors and Experiences

Question
I am a 21 F, Last period Feb 22.
Hi, I just miscarried 6 days ago. I was supposed to be 11 weeks pregnant and the ultrasound showed my baby was only measuring 8.5 weeks w/ no heartbeat. When I went for my first app. at 7 weeks my baby had a heartbeat of 140 bpm. I spotted at 8 weeks and went in for another ultrasound the babys heartbeat then was 170 bpm. My question is this.. I have heard that once u have a strong heartbeat the risk of miscarriage drops. With such a strong heartbeat at 7 and 8 weeks what could be the reasons a miscarriage occured? And what were my odds of miscarrying after my baby having a strong heartbeat?  

Answer
Once you have a strong fetal heartbeat, the risk of miscarriage drops from 15-20% tp around 5%. the risk drops, but does not disappear. There is nothing you can do to  cause a miscarriage and there is nothing you can do to  prevent a miscarriage, especially at 6-8 weeks from your last period.